diff options
Diffstat (limited to 'drivers/tty/tty_ldisc.c')
| -rw-r--r-- | drivers/tty/tty_ldisc.c | 1027 |
1 files changed, 435 insertions, 592 deletions
diff --git a/drivers/tty/tty_ldisc.c b/drivers/tty/tty_ldisc.c index 1afe192bef6a..d80e9d4c974b 100644 --- a/drivers/tty/tty_ldisc.c +++ b/drivers/tty/tty_ldisc.c @@ -1,3 +1,4 @@ +// SPDX-License-Identifier: GPL-2.0 #include <linux/types.h> #include <linux/errno.h> #include <linux/kmod.h> @@ -11,7 +12,6 @@ #include <linux/slab.h> #include <linux/poll.h> #include <linux/proc_fs.h> -#include <linux/init.h> #include <linux/module.h> #include <linux/device.h> #include <linux/wait.h> @@ -19,88 +19,74 @@ #include <linux/seq_file.h> #include <linux/uaccess.h> #include <linux/ratelimit.h> +#include "tty.h" #undef LDISC_DEBUG_HANGUP #ifdef LDISC_DEBUG_HANGUP -#define tty_ldisc_debug(tty, f, args...) ({ \ - char __b[64]; \ - printk(KERN_DEBUG "%s: %s: " f, __func__, tty_name(tty, __b), ##args); \ -}) +#define tty_ldisc_debug(tty, f, args...) tty_debug(tty, f, ##args) #else #define tty_ldisc_debug(tty, f, args...) #endif +/* lockdep nested classes for tty->ldisc_sem */ +enum { + LDISC_SEM_NORMAL, + LDISC_SEM_OTHER, +}; + + /* * This guards the refcounted line discipline lists. The lock * must be taken with irqs off because there are hangup path * callers who will do ldisc lookups and cannot sleep. */ -static DEFINE_RAW_SPINLOCK(tty_ldisc_lock); -static DECLARE_WAIT_QUEUE_HEAD(tty_ldisc_wait); +static DEFINE_RAW_SPINLOCK(tty_ldiscs_lock); /* Line disc dispatch table */ static struct tty_ldisc_ops *tty_ldiscs[NR_LDISCS]; /** - * tty_register_ldisc - install a line discipline - * @disc: ldisc number - * @new_ldisc: pointer to the ldisc object + * tty_register_ldisc - install a line discipline + * @new_ldisc: pointer to the ldisc object * - * Installs a new line discipline into the kernel. The discipline - * is set up as unreferenced and then made available to the kernel - * from this point onwards. + * Installs a new line discipline into the kernel. The discipline is set up as + * unreferenced and then made available to the kernel from this point onwards. * - * Locking: - * takes tty_ldisc_lock to guard against ldisc races + * Locking: takes %tty_ldiscs_lock to guard against ldisc races */ - -int tty_register_ldisc(int disc, struct tty_ldisc_ops *new_ldisc) +int tty_register_ldisc(struct tty_ldisc_ops *new_ldisc) { unsigned long flags; - int ret = 0; - if (disc < N_TTY || disc >= NR_LDISCS) + if (new_ldisc->num < N_TTY || new_ldisc->num >= NR_LDISCS) return -EINVAL; - raw_spin_lock_irqsave(&tty_ldisc_lock, flags); - tty_ldiscs[disc] = new_ldisc; - new_ldisc->num = disc; - new_ldisc->refcount = 0; - raw_spin_unlock_irqrestore(&tty_ldisc_lock, flags); + raw_spin_lock_irqsave(&tty_ldiscs_lock, flags); + tty_ldiscs[new_ldisc->num] = new_ldisc; + raw_spin_unlock_irqrestore(&tty_ldiscs_lock, flags); - return ret; + return 0; } EXPORT_SYMBOL(tty_register_ldisc); /** - * tty_unregister_ldisc - unload a line discipline - * @disc: ldisc number - * @new_ldisc: pointer to the ldisc object + * tty_unregister_ldisc - unload a line discipline + * @ldisc: ldisc number * - * Remove a line discipline from the kernel providing it is not - * currently in use. + * Remove a line discipline from the kernel providing it is not currently in + * use. * - * Locking: - * takes tty_ldisc_lock to guard against ldisc races + * Locking: takes %tty_ldiscs_lock to guard against ldisc races */ -int tty_unregister_ldisc(int disc) +void tty_unregister_ldisc(struct tty_ldisc_ops *ldisc) { unsigned long flags; - int ret = 0; - if (disc < N_TTY || disc >= NR_LDISCS) - return -EINVAL; - - raw_spin_lock_irqsave(&tty_ldisc_lock, flags); - if (tty_ldiscs[disc]->refcount) - ret = -EBUSY; - else - tty_ldiscs[disc] = NULL; - raw_spin_unlock_irqrestore(&tty_ldisc_lock, flags); - - return ret; + raw_spin_lock_irqsave(&tty_ldiscs_lock, flags); + tty_ldiscs[ldisc->num] = NULL; + raw_spin_unlock_irqrestore(&tty_ldiscs_lock, flags); } EXPORT_SYMBOL(tty_unregister_ldisc); @@ -109,17 +95,15 @@ static struct tty_ldisc_ops *get_ldops(int disc) unsigned long flags; struct tty_ldisc_ops *ldops, *ret; - raw_spin_lock_irqsave(&tty_ldisc_lock, flags); + raw_spin_lock_irqsave(&tty_ldiscs_lock, flags); ret = ERR_PTR(-EINVAL); ldops = tty_ldiscs[disc]; if (ldops) { ret = ERR_PTR(-EAGAIN); - if (try_module_get(ldops->owner)) { - ldops->refcount++; + if (try_module_get(ldops->owner)) ret = ldops; - } } - raw_spin_unlock_irqrestore(&tty_ldisc_lock, flags); + raw_spin_unlock_irqrestore(&tty_ldiscs_lock, flags); return ret; } @@ -127,26 +111,32 @@ static void put_ldops(struct tty_ldisc_ops *ldops) { unsigned long flags; - raw_spin_lock_irqsave(&tty_ldisc_lock, flags); - ldops->refcount--; + raw_spin_lock_irqsave(&tty_ldiscs_lock, flags); module_put(ldops->owner); - raw_spin_unlock_irqrestore(&tty_ldisc_lock, flags); + raw_spin_unlock_irqrestore(&tty_ldiscs_lock, flags); } +int tty_ldisc_autoload = IS_BUILTIN(CONFIG_LDISC_AUTOLOAD); + /** - * tty_ldisc_get - take a reference to an ldisc - * @disc: ldisc number - * - * Takes a reference to a line discipline. Deals with refcounts and - * module locking counts. Returns NULL if the discipline is not available. - * Returns a pointer to the discipline and bumps the ref count if it is - * available - * - * Locking: - * takes tty_ldisc_lock to guard against ldisc races + * tty_ldisc_get - take a reference to an ldisc + * @tty: tty device + * @disc: ldisc number + * + * Takes a reference to a line discipline. Deals with refcounts and module + * locking counts. If the discipline is not available, its module loaded, if + * possible. + * + * Returns: + * * -%EINVAL if the discipline index is not [%N_TTY .. %NR_LDISCS] or if the + * discipline is not registered + * * -%EAGAIN if request_module() failed to load or register the discipline + * * -%ENOMEM if allocation failure + * * Otherwise, returns a pointer to the discipline and bumps the ref count + * + * Locking: takes %tty_ldiscs_lock to guard against ldisc races */ - -static struct tty_ldisc *tty_ldisc_get(int disc) +static struct tty_ldisc *tty_ldisc_get(struct tty_struct *tty, int disc) { struct tty_ldisc *ld; struct tty_ldisc_ops *ldops; @@ -160,46 +150,38 @@ static struct tty_ldisc *tty_ldisc_get(int disc) */ ldops = get_ldops(disc); if (IS_ERR(ldops)) { + if (!capable(CAP_SYS_MODULE) && !tty_ldisc_autoload) + return ERR_PTR(-EPERM); request_module("tty-ldisc-%d", disc); ldops = get_ldops(disc); if (IS_ERR(ldops)) return ERR_CAST(ldops); } - ld = kmalloc(sizeof(struct tty_ldisc), GFP_KERNEL); - if (ld == NULL) { - put_ldops(ldops); - return ERR_PTR(-ENOMEM); - } - + /* + * There is no way to handle allocation failure of only 16 bytes. + * Let's simplify error handling and save more memory. + */ + ld = kmalloc(sizeof(struct tty_ldisc), GFP_KERNEL | __GFP_NOFAIL); ld->ops = ldops; - atomic_set(&ld->users, 1); - init_waitqueue_head(&ld->wq_idle); + ld->tty = tty; return ld; } /** - * tty_ldisc_put - release the ldisc + * tty_ldisc_put - release the ldisc + * @ld: lisdsc to release * - * Complement of tty_ldisc_get(). + * Complement of tty_ldisc_get(). */ -static inline void tty_ldisc_put(struct tty_ldisc *ld) +static void tty_ldisc_put(struct tty_ldisc *ld) { - unsigned long flags; - if (WARN_ON_ONCE(!ld)) return; - raw_spin_lock_irqsave(&tty_ldisc_lock, flags); - - /* unreleased reader reference(s) will cause this WARN */ - WARN_ON(!atomic_dec_and_test(&ld->users)); - - ld->ops->refcount--; - module_put(ld->ops->owner); + put_ldops(ld->ops); kfree(ld); - raw_spin_unlock_irqrestore(&tty_ldisc_lock, flags); } static void *tty_ldiscs_seq_start(struct seq_file *m, loff_t *pos) @@ -230,588 +212,489 @@ static int tty_ldiscs_seq_show(struct seq_file *m, void *v) return 0; } -static const struct seq_operations tty_ldiscs_seq_ops = { +const struct seq_operations tty_ldiscs_seq_ops = { .start = tty_ldiscs_seq_start, .next = tty_ldiscs_seq_next, .stop = tty_ldiscs_seq_stop, .show = tty_ldiscs_seq_show, }; -static int proc_tty_ldiscs_open(struct inode *inode, struct file *file) -{ - return seq_open(file, &tty_ldiscs_seq_ops); -} - -const struct file_operations tty_ldiscs_proc_fops = { - .owner = THIS_MODULE, - .open = proc_tty_ldiscs_open, - .read = seq_read, - .llseek = seq_lseek, - .release = seq_release, -}; - /** - * tty_ldisc_try - internal helper - * @tty: the tty - * - * Make a single attempt to grab and bump the refcount on - * the tty ldisc. Return 0 on failure or 1 on success. This is - * used to implement both the waiting and non waiting versions - * of tty_ldisc_ref + * tty_ldisc_ref_wait - wait for the tty ldisc + * @tty: tty device * - * Locking: takes tty_ldisc_lock - */ - -static struct tty_ldisc *tty_ldisc_try(struct tty_struct *tty) -{ - unsigned long flags; - struct tty_ldisc *ld; - - /* FIXME: this allows reference acquire after TTY_LDISC is cleared */ - raw_spin_lock_irqsave(&tty_ldisc_lock, flags); - ld = NULL; - if (test_bit(TTY_LDISC, &tty->flags) && tty->ldisc) { - ld = tty->ldisc; - atomic_inc(&ld->users); - } - raw_spin_unlock_irqrestore(&tty_ldisc_lock, flags); - return ld; -} - -/** - * tty_ldisc_ref_wait - wait for the tty ldisc - * @tty: tty device + * Dereference the line discipline for the terminal and take a reference to it. + * If the line discipline is in flux then wait patiently until it changes. * - * Dereference the line discipline for the terminal and take a - * reference to it. If the line discipline is in flux then - * wait patiently until it changes. + * Returns: %NULL if the tty has been hungup and not re-opened with a new file + * descriptor, otherwise valid ldisc reference * - * Note: Must not be called from an IRQ/timer context. The caller - * must also be careful not to hold other locks that will deadlock - * against a discipline change, such as an existing ldisc reference - * (which we check for) + * Note 1: Must not be called from an IRQ/timer context. The caller must also + * be careful not to hold other locks that will deadlock against a discipline + * change, such as an existing ldisc reference (which we check for). * - * Locking: call functions take tty_ldisc_lock + * Note 2: a file_operations routine (read/poll/write) should use this function + * to wait for any ldisc lifetime events to finish. */ - struct tty_ldisc *tty_ldisc_ref_wait(struct tty_struct *tty) { struct tty_ldisc *ld; - /* wait_event is a macro */ - wait_event(tty_ldisc_wait, (ld = tty_ldisc_try(tty)) != NULL); + ldsem_down_read(&tty->ldisc_sem, MAX_SCHEDULE_TIMEOUT); + ld = tty->ldisc; + if (!ld) + ldsem_up_read(&tty->ldisc_sem); return ld; } EXPORT_SYMBOL_GPL(tty_ldisc_ref_wait); /** - * tty_ldisc_ref - get the tty ldisc - * @tty: tty device + * tty_ldisc_ref - get the tty ldisc + * @tty: tty device * - * Dereference the line discipline for the terminal and take a - * reference to it. If the line discipline is in flux then - * return NULL. Can be called from IRQ and timer functions. - * - * Locking: called functions take tty_ldisc_lock + * Dereference the line discipline for the terminal and take a reference to it. + * If the line discipline is in flux then return %NULL. Can be called from IRQ + * and timer functions. */ - struct tty_ldisc *tty_ldisc_ref(struct tty_struct *tty) { - return tty_ldisc_try(tty); + struct tty_ldisc *ld = NULL; + + if (ldsem_down_read_trylock(&tty->ldisc_sem)) { + ld = tty->ldisc; + if (!ld) + ldsem_up_read(&tty->ldisc_sem); + } + return ld; } EXPORT_SYMBOL_GPL(tty_ldisc_ref); /** - * tty_ldisc_deref - free a tty ldisc reference - * @ld: reference to free up + * tty_ldisc_deref - free a tty ldisc reference + * @ld: reference to free up * - * Undoes the effect of tty_ldisc_ref or tty_ldisc_ref_wait. May - * be called in IRQ context. - * - * Locking: takes tty_ldisc_lock + * Undoes the effect of tty_ldisc_ref() or tty_ldisc_ref_wait(). May be called + * in IRQ context. */ - void tty_ldisc_deref(struct tty_ldisc *ld) { - unsigned long flags; + ldsem_up_read(&ld->tty->ldisc_sem); +} +EXPORT_SYMBOL_GPL(tty_ldisc_deref); - if (WARN_ON_ONCE(!ld)) - return; - raw_spin_lock_irqsave(&tty_ldisc_lock, flags); - /* - * WARNs if one-too-many reader references were released - * - the last reference must be released with tty_ldisc_put - */ - WARN_ON(atomic_dec_and_test(&ld->users)); - raw_spin_unlock_irqrestore(&tty_ldisc_lock, flags); +static inline int +__tty_ldisc_lock(struct tty_struct *tty, unsigned long timeout) +{ + return ldsem_down_write(&tty->ldisc_sem, timeout); +} - if (waitqueue_active(&ld->wq_idle)) - wake_up(&ld->wq_idle); +static inline int +__tty_ldisc_lock_nested(struct tty_struct *tty, unsigned long timeout) +{ + return ldsem_down_write_nested(&tty->ldisc_sem, + LDISC_SEM_OTHER, timeout); } -EXPORT_SYMBOL_GPL(tty_ldisc_deref); -/** - * tty_ldisc_enable - allow ldisc use - * @tty: terminal to activate ldisc on - * - * Set the TTY_LDISC flag when the line discipline can be called - * again. Do necessary wakeups for existing sleepers. Clear the LDISC - * changing flag to indicate any ldisc change is now over. - * - * Note: nobody should set the TTY_LDISC bit except via this function. - * Clearing directly is allowed. - */ +static inline void __tty_ldisc_unlock(struct tty_struct *tty) +{ + ldsem_up_write(&tty->ldisc_sem); +} -static void tty_ldisc_enable(struct tty_struct *tty) +int tty_ldisc_lock(struct tty_struct *tty, unsigned long timeout) +{ + int ret; + + /* Kindly asking blocked readers to release the read side */ + set_bit(TTY_LDISC_CHANGING, &tty->flags); + wake_up_interruptible_all(&tty->read_wait); + wake_up_interruptible_all(&tty->write_wait); + + ret = __tty_ldisc_lock(tty, timeout); + if (!ret) + return -EBUSY; + set_bit(TTY_LDISC_HALTED, &tty->flags); + return 0; +} + +void tty_ldisc_unlock(struct tty_struct *tty) { clear_bit(TTY_LDISC_HALTED, &tty->flags); - set_bit(TTY_LDISC, &tty->flags); + /* Can be cleared here - ldisc_unlock will wake up writers firstly */ clear_bit(TTY_LDISC_CHANGING, &tty->flags); - wake_up(&tty_ldisc_wait); + __tty_ldisc_unlock(tty); +} + +static int +tty_ldisc_lock_pair_timeout(struct tty_struct *tty, struct tty_struct *tty2, + unsigned long timeout) +{ + int ret; + + if (tty < tty2) { + ret = __tty_ldisc_lock(tty, timeout); + if (ret) { + ret = __tty_ldisc_lock_nested(tty2, timeout); + if (!ret) + __tty_ldisc_unlock(tty); + } + } else { + /* if this is possible, it has lots of implications */ + WARN_ON_ONCE(tty == tty2); + if (tty2 && tty != tty2) { + ret = __tty_ldisc_lock(tty2, timeout); + if (ret) { + ret = __tty_ldisc_lock_nested(tty, timeout); + if (!ret) + __tty_ldisc_unlock(tty2); + } + } else + ret = __tty_ldisc_lock(tty, timeout); + } + + if (!ret) + return -EBUSY; + + set_bit(TTY_LDISC_HALTED, &tty->flags); + if (tty2) + set_bit(TTY_LDISC_HALTED, &tty2->flags); + return 0; +} + +static void tty_ldisc_lock_pair(struct tty_struct *tty, struct tty_struct *tty2) +{ + tty_ldisc_lock_pair_timeout(tty, tty2, MAX_SCHEDULE_TIMEOUT); +} + +static void tty_ldisc_unlock_pair(struct tty_struct *tty, + struct tty_struct *tty2) +{ + __tty_ldisc_unlock(tty); + if (tty2) + __tty_ldisc_unlock(tty2); } /** - * tty_ldisc_flush - flush line discipline queue - * @tty: tty + * tty_ldisc_flush - flush line discipline queue + * @tty: tty to flush ldisc for * - * Flush the line discipline queue (if any) for this tty. If there - * is no line discipline active this is a no-op. + * Flush the line discipline queue (if any) and the tty flip buffers for this + * @tty. */ - void tty_ldisc_flush(struct tty_struct *tty) { struct tty_ldisc *ld = tty_ldisc_ref(tty); - if (ld) { - if (ld->ops->flush_buffer) - ld->ops->flush_buffer(tty); + + tty_buffer_flush(tty, ld); + if (ld) tty_ldisc_deref(ld); - } - tty_buffer_flush(tty); } EXPORT_SYMBOL_GPL(tty_ldisc_flush); /** - * tty_set_termios_ldisc - set ldisc field - * @tty: tty structure - * @num: line discipline number + * tty_set_termios_ldisc - set ldisc field + * @tty: tty structure + * @disc: line discipline number + * + * This is probably overkill for real world processors but they are not on hot + * paths so a little discipline won't do any harm. * - * This is probably overkill for real world processors but - * they are not on hot paths so a little discipline won't do - * any harm. + * The line discipline-related tty_struct fields are reset to prevent the ldisc + * driver from re-using stale information for the new ldisc instance. * - * Locking: takes termios_mutex + * Locking: takes termios_rwsem */ - -static void tty_set_termios_ldisc(struct tty_struct *tty, int num) +static void tty_set_termios_ldisc(struct tty_struct *tty, int disc) { - mutex_lock(&tty->termios_mutex); - tty->termios.c_line = num; - mutex_unlock(&tty->termios_mutex); + down_write(&tty->termios_rwsem); + tty->termios.c_line = disc; + up_write(&tty->termios_rwsem); + + tty->disc_data = NULL; + tty->receive_room = 0; } /** - * tty_ldisc_open - open a line discipline - * @tty: tty we are opening the ldisc on - * @ld: discipline to open + * tty_ldisc_open - open a line discipline + * @tty: tty we are opening the ldisc on + * @ld: discipline to open * - * A helper opening method. Also a convenient debugging and check - * point. + * A helper opening method. Also a convenient debugging and check point. * - * Locking: always called with BTM already held. + * Locking: always called with BTM already held. */ - static int tty_ldisc_open(struct tty_struct *tty, struct tty_ldisc *ld) { WARN_ON(test_and_set_bit(TTY_LDISC_OPEN, &tty->flags)); if (ld->ops->open) { int ret; - /* BTM here locks versus a hangup event */ + /* BTM here locks versus a hangup event */ ret = ld->ops->open(tty); if (ret) clear_bit(TTY_LDISC_OPEN, &tty->flags); + + tty_ldisc_debug(tty, "%p: opened\n", ld); return ret; } return 0; } /** - * tty_ldisc_close - close a line discipline - * @tty: tty we are opening the ldisc on - * @ld: discipline to close + * tty_ldisc_close - close a line discipline + * @tty: tty we are opening the ldisc on + * @ld: discipline to close * - * A helper close method. Also a convenient debugging and check - * point. + * A helper close method. Also a convenient debugging and check point. */ - static void tty_ldisc_close(struct tty_struct *tty, struct tty_ldisc *ld) { + lockdep_assert_held_write(&tty->ldisc_sem); WARN_ON(!test_bit(TTY_LDISC_OPEN, &tty->flags)); clear_bit(TTY_LDISC_OPEN, &tty->flags); if (ld->ops->close) ld->ops->close(tty); + tty_ldisc_debug(tty, "%p: closed\n", ld); } /** - * tty_ldisc_restore - helper for tty ldisc change - * @tty: tty to recover - * @old: previous ldisc + * tty_ldisc_failto - helper for ldisc failback + * @tty: tty to open the ldisc on + * @ld: ldisc we are trying to fail back to * - * Restore the previous line discipline or N_TTY when a line discipline - * change fails due to an open error + * Helper to try and recover a tty when switching back to the old ldisc fails + * and we need something attached. */ - -static void tty_ldisc_restore(struct tty_struct *tty, struct tty_ldisc *old) +static int tty_ldisc_failto(struct tty_struct *tty, int ld) { - char buf[64]; - struct tty_ldisc *new_ldisc; + struct tty_ldisc *disc = tty_ldisc_get(tty, ld); int r; - /* There is an outstanding reference here so this is safe */ - old = tty_ldisc_get(old->ops->num); - WARN_ON(IS_ERR(old)); - tty->ldisc = old; - tty_set_termios_ldisc(tty, old->ops->num); - if (tty_ldisc_open(tty, old) < 0) { - tty_ldisc_put(old); - /* This driver is always present */ - new_ldisc = tty_ldisc_get(N_TTY); - if (IS_ERR(new_ldisc)) - panic("n_tty: get"); - tty->ldisc = new_ldisc; - tty_set_termios_ldisc(tty, N_TTY); - r = tty_ldisc_open(tty, new_ldisc); - if (r < 0) - panic("Couldn't open N_TTY ldisc for " - "%s --- error %d.", - tty_name(tty, buf), r); - } -} - -/** - * tty_ldisc_wait_idle - wait for the ldisc to become idle - * @tty: tty to wait for - * @timeout: for how long to wait at most - * - * Wait for the line discipline to become idle. The discipline must - * have been halted for this to guarantee it remains idle. - */ -static int tty_ldisc_wait_idle(struct tty_struct *tty, long timeout) -{ - long ret; - ret = wait_event_timeout(tty->ldisc->wq_idle, - atomic_read(&tty->ldisc->users) == 1, timeout); - return ret > 0 ? 0 : -EBUSY; -} - -/** - * tty_ldisc_halt - shut down the line discipline - * @tty: tty device - * @o_tty: paired pty device (can be NULL) - * @timeout: # of jiffies to wait for ldisc refs to be released - * - * Shut down the line discipline and work queue for this tty device and - * its paired pty (if exists). Clearing the TTY_LDISC flag ensures - * no further references can be obtained, while waiting for existing - * references to be released ensures no more data is fed to the ldisc. - * - * You need to do a 'flush_scheduled_work()' (outside the ldisc_mutex) - * in order to make sure any currently executing ldisc work is also - * flushed. - */ - -static int tty_ldisc_halt(struct tty_struct *tty, struct tty_struct *o_tty, - long timeout) -{ - int retval; - - clear_bit(TTY_LDISC, &tty->flags); - if (o_tty) - clear_bit(TTY_LDISC, &o_tty->flags); - - retval = tty_ldisc_wait_idle(tty, timeout); - if (!retval && o_tty) - retval = tty_ldisc_wait_idle(o_tty, timeout); - if (retval) - return retval; - - set_bit(TTY_LDISC_HALTED, &tty->flags); - if (o_tty) - set_bit(TTY_LDISC_HALTED, &o_tty->flags); - - return 0; + lockdep_assert_held_write(&tty->ldisc_sem); + if (IS_ERR(disc)) + return PTR_ERR(disc); + tty->ldisc = disc; + tty_set_termios_ldisc(tty, ld); + r = tty_ldisc_open(tty, disc); + if (r < 0) + tty_ldisc_put(disc); + return r; } /** - * tty_ldisc_hangup_halt - halt the line discipline for hangup - * @tty: tty being hung up - * - * Shut down the line discipline and work queue for the tty device - * being hungup. Clear the TTY_LDISC flag to ensure no further - * references can be obtained and wait for remaining references to be - * released to ensure no more data is fed to this ldisc. - * Caller must hold legacy and ->ldisc_mutex. + * tty_ldisc_restore - helper for tty ldisc change + * @tty: tty to recover + * @old: previous ldisc * - * NB: tty_set_ldisc() is prevented from changing the ldisc concurrently - * with this function by checking the TTY_HUPPING flag. + * Restore the previous line discipline or %N_TTY when a line discipline change + * fails due to an open error */ -static bool tty_ldisc_hangup_halt(struct tty_struct *tty) +static void tty_ldisc_restore(struct tty_struct *tty, struct tty_ldisc *old) { - char cur_n[TASK_COMM_LEN], tty_n[64]; - long timeout = 3 * HZ; - - clear_bit(TTY_LDISC, &tty->flags); - - if (tty->ldisc) { /* Not yet closed */ - tty_unlock(tty); - - while (tty_ldisc_wait_idle(tty, timeout) == -EBUSY) { - timeout = MAX_SCHEDULE_TIMEOUT; - printk_ratelimited(KERN_WARNING - "%s: waiting (%s) for %s took too long, but we keep waiting...\n", - __func__, get_task_comm(cur_n, current), - tty_name(tty, tty_n)); - } - - set_bit(TTY_LDISC_HALTED, &tty->flags); - - /* must reacquire both locks and preserve lock order */ - mutex_unlock(&tty->ldisc_mutex); - tty_lock(tty); - mutex_lock(&tty->ldisc_mutex); + /* There is an outstanding reference here so this is safe */ + if (tty_ldisc_failto(tty, old->ops->num) < 0) { + const char *name = tty_name(tty); + + pr_warn("Falling back ldisc for %s.\n", name); + /* + * The traditional behaviour is to fall back to N_TTY, we + * want to avoid falling back to N_NULL unless we have no + * choice to avoid the risk of breaking anything + */ + if (tty_ldisc_failto(tty, N_TTY) < 0 && + tty_ldisc_failto(tty, N_NULL) < 0) + panic("Couldn't open N_NULL ldisc for %s.", name); } - return !!tty->ldisc; } /** - * tty_set_ldisc - set line discipline - * @tty: the terminal to set - * @ldisc: the line discipline - * - * Set the discipline of a tty line. Must be called from a process - * context. The ldisc change logic has to protect itself against any - * overlapping ldisc change (including on the other end of pty pairs), - * the close of one side of a tty/pty pair, and eventually hangup. - * - * Locking: takes tty_ldisc_lock, termios_mutex + * tty_set_ldisc - set line discipline + * @tty: the terminal to set + * @disc: the line discipline number + * + * Set the discipline of a tty line. Must be called from a process context. The + * ldisc change logic has to protect itself against any overlapping ldisc + * change (including on the other end of pty pairs), the close of one side of a + * tty/pty pair, and eventually hangup. */ - -int tty_set_ldisc(struct tty_struct *tty, int ldisc) +int tty_set_ldisc(struct tty_struct *tty, int disc) { int retval; - struct tty_ldisc *o_ldisc, *new_ldisc; - struct tty_struct *o_tty; + struct tty_ldisc *old_ldisc, *new_ldisc; - new_ldisc = tty_ldisc_get(ldisc); + new_ldisc = tty_ldisc_get(tty, disc); if (IS_ERR(new_ldisc)) return PTR_ERR(new_ldisc); tty_lock(tty); - /* - * We need to look at the tty locking here for pty/tty pairs - * when both sides try to change in parallel. - */ - - o_tty = tty->link; /* o_tty is the pty side or NULL */ - - - /* - * Check the no-op case - */ + retval = tty_ldisc_lock(tty, 5 * HZ); + if (retval) + goto err; - if (tty->ldisc->ops->num == ldisc) { - tty_unlock(tty); - tty_ldisc_put(new_ldisc); - return 0; + if (!tty->ldisc) { + retval = -EIO; + goto out; } - mutex_lock(&tty->ldisc_mutex); - - /* - * We could be midstream of another ldisc change which has - * dropped the lock during processing. If so we need to wait. - */ + /* Check the no-op case */ + if (tty->ldisc->ops->num == disc) + goto out; - while (test_bit(TTY_LDISC_CHANGING, &tty->flags)) { - mutex_unlock(&tty->ldisc_mutex); - tty_unlock(tty); - wait_event(tty_ldisc_wait, - test_bit(TTY_LDISC_CHANGING, &tty->flags) == 0); - tty_lock(tty); - mutex_lock(&tty->ldisc_mutex); + if (test_bit(TTY_HUPPED, &tty->flags)) { + /* We were raced by hangup */ + retval = -EIO; + goto out; } - set_bit(TTY_LDISC_CHANGING, &tty->flags); - - /* - * No more input please, we are switching. The new ldisc - * will update this value in the ldisc open function - */ - - tty->receive_room = 0; - - o_ldisc = tty->ldisc; - - tty_unlock(tty); - /* - * Make sure we don't change while someone holds a - * reference to the line discipline. The TTY_LDISC bit - * prevents anyone taking a reference once it is clear. - * We need the lock to avoid racing reference takers. - * - * We must clear the TTY_LDISC bit here to avoid a livelock - * with a userspace app continually trying to use the tty in - * parallel to the change and re-referencing the tty. - */ - - retval = tty_ldisc_halt(tty, o_tty, 5 * HZ); - - /* - * Wait for hangup to complete, if pending. - * We must drop the mutex here in case a hangup is also in process. - */ - - mutex_unlock(&tty->ldisc_mutex); - - flush_work(&tty->hangup_work); - - tty_lock(tty); - mutex_lock(&tty->ldisc_mutex); - - /* handle wait idle failure locked */ - if (retval) { - tty_ldisc_put(new_ldisc); - goto enable; + if (tty->ops->ldisc_ok) { + retval = tty->ops->ldisc_ok(tty, disc); + if (retval) + goto out; } - if (test_bit(TTY_HUPPING, &tty->flags)) { - /* We were raced by the hangup method. It will have stomped - the ldisc data and closed the ldisc down */ - clear_bit(TTY_LDISC_CHANGING, &tty->flags); - mutex_unlock(&tty->ldisc_mutex); - tty_ldisc_put(new_ldisc); - tty_unlock(tty); - return -EIO; - } + old_ldisc = tty->ldisc; - /* Shutdown the current discipline. */ - tty_ldisc_close(tty, o_ldisc); + /* Shutdown the old discipline. */ + tty_ldisc_close(tty, old_ldisc); /* Now set up the new line discipline. */ tty->ldisc = new_ldisc; - tty_set_termios_ldisc(tty, ldisc); + tty_set_termios_ldisc(tty, disc); retval = tty_ldisc_open(tty, new_ldisc); if (retval < 0) { /* Back to the old one or N_TTY if we can't */ tty_ldisc_put(new_ldisc); - tty_ldisc_restore(tty, o_ldisc); + tty_ldisc_restore(tty, old_ldisc); } - /* At this point we hold a reference to the new ldisc and a - a reference to the old ldisc. If we ended up flipping back - to the existing ldisc we have two references to it */ - - if (tty->ldisc->ops->num != o_ldisc->ops->num && tty->ops->set_ldisc) + if (tty->ldisc->ops->num != old_ldisc->ops->num && tty->ops->set_ldisc) { + down_read(&tty->termios_rwsem); tty->ops->set_ldisc(tty); + up_read(&tty->termios_rwsem); + } - tty_ldisc_put(o_ldisc); - -enable: /* - * Allow ldisc referencing to occur again + * At this point we hold a reference to the new ldisc and a + * reference to the old ldisc, or we hold two references to + * the old ldisc (if it was restored as part of error cleanup + * above). In either case, releasing a single reference from + * the old ldisc is correct. */ + new_ldisc = old_ldisc; +out: + tty_ldisc_unlock(tty); - tty_ldisc_enable(tty); - if (o_tty) - tty_ldisc_enable(o_tty); - - /* Restart the work queue in case no characters kick it off. Safe if - already running */ - schedule_work(&tty->port->buf.work); - if (o_tty) - schedule_work(&o_tty->port->buf.work); - - mutex_unlock(&tty->ldisc_mutex); + /* + * Restart the work queue in case no characters kick it off. Safe if + * already running + */ + tty_buffer_restart_work(tty->port); +err: + tty_ldisc_put(new_ldisc); /* drop the extra reference */ tty_unlock(tty); return retval; } +EXPORT_SYMBOL_GPL(tty_set_ldisc); /** - * tty_reset_termios - reset terminal state - * @tty: tty to reset + * tty_ldisc_kill - teardown ldisc + * @tty: tty being released * - * Restore a terminal to the driver default state. + * Perform final close of the ldisc and reset @tty->ldisc */ +static void tty_ldisc_kill(struct tty_struct *tty) +{ + lockdep_assert_held_write(&tty->ldisc_sem); + if (!tty->ldisc) + return; + /* + * Now kill off the ldisc + */ + tty_ldisc_close(tty, tty->ldisc); + tty_ldisc_put(tty->ldisc); + /* Force an oops if we mess this up */ + tty->ldisc = NULL; +} +/** + * tty_reset_termios - reset terminal state + * @tty: tty to reset + * + * Restore a terminal to the driver default state. + */ static void tty_reset_termios(struct tty_struct *tty) { - mutex_lock(&tty->termios_mutex); + down_write(&tty->termios_rwsem); tty->termios = tty->driver->init_termios; tty->termios.c_ispeed = tty_termios_input_baud_rate(&tty->termios); tty->termios.c_ospeed = tty_termios_baud_rate(&tty->termios); - mutex_unlock(&tty->termios_mutex); + up_write(&tty->termios_rwsem); } /** - * tty_ldisc_reinit - reinitialise the tty ldisc - * @tty: tty to reinit - * @ldisc: line discipline to reinitialize + * tty_ldisc_reinit - reinitialise the tty ldisc + * @tty: tty to reinit + * @disc: line discipline to reinitialize + * + * Completely reinitialize the line discipline state, by closing the current + * instance, if there is one, and opening a new instance. If an error occurs + * opening the new non-%N_TTY instance, the instance is dropped and @tty->ldisc + * reset to %NULL. The caller can then retry with %N_TTY instead. * - * Switch the tty to a line discipline and leave the ldisc - * state closed + * Returns: 0 if successful, otherwise error code < 0 */ - -static int tty_ldisc_reinit(struct tty_struct *tty, int ldisc) +int tty_ldisc_reinit(struct tty_struct *tty, int disc) { - struct tty_ldisc *ld = tty_ldisc_get(ldisc); + struct tty_ldisc *ld; + int retval; - if (IS_ERR(ld)) - return -1; + lockdep_assert_held_write(&tty->ldisc_sem); + ld = tty_ldisc_get(tty, disc); + if (IS_ERR(ld)) { + BUG_ON(disc == N_TTY); + return PTR_ERR(ld); + } - tty_ldisc_close(tty, tty->ldisc); - tty_ldisc_put(tty->ldisc); - /* - * Switch the line discipline back - */ - tty->ldisc = ld; - tty_set_termios_ldisc(tty, ldisc); + if (tty->ldisc) { + tty_ldisc_close(tty, tty->ldisc); + tty_ldisc_put(tty->ldisc); + } - return 0; + /* switch the line discipline */ + tty->ldisc = ld; + tty_set_termios_ldisc(tty, disc); + retval = tty_ldisc_open(tty, tty->ldisc); + if (retval) { + tty_ldisc_put(tty->ldisc); + tty->ldisc = NULL; + } + return retval; } /** - * tty_ldisc_hangup - hangup ldisc reset - * @tty: tty being hung up + * tty_ldisc_hangup - hangup ldisc reset + * @tty: tty being hung up + * @reinit: whether to re-initialise the tty * - * Some tty devices reset their termios when they receive a hangup - * event. In that situation we must also switch back to N_TTY properly - * before we reset the termios data. + * Some tty devices reset their termios when they receive a hangup event. In + * that situation we must also switch back to %N_TTY properly before we reset + * the termios data. * - * Locking: We can take the ldisc mutex as the rest of the code is - * careful to allow for this. + * Locking: We can take the ldisc mutex as the rest of the code is careful to + * allow for this. * - * In the pty pair case this occurs in the close() path of the - * tty itself so we must be careful about locking rules. + * In the pty pair case this occurs in the close() path of the tty itself so we + * must be careful about locking rules. */ - -void tty_ldisc_hangup(struct tty_struct *tty) +void tty_ldisc_hangup(struct tty_struct *tty, bool reinit) { struct tty_ldisc *ld; - int reset = tty->driver->flags & TTY_DRIVER_RESET_TERMIOS; - int err = 0; - tty_ldisc_debug(tty, "closing ldisc: %p\n", tty->ldisc); + tty_ldisc_debug(tty, "%p: hangup\n", tty->ldisc); - /* - * FIXME! What are the locking issues here? This may me overdoing - * things... This question is especially important now that we've - * removed the irqlock. - */ ld = tty_ldisc_ref(tty); if (ld != NULL) { - /* We may have no line discipline at this point */ if (ld->ops->flush_buffer) ld->ops->flush_buffer(tty); tty_driver_flush_buffer(tty); @@ -822,160 +705,120 @@ void tty_ldisc_hangup(struct tty_struct *tty) ld->ops->hangup(tty); tty_ldisc_deref(ld); } - /* - * FIXME: Once we trust the LDISC code better we can wait here for - * ldisc completion and fix the driver call race - */ - wake_up_interruptible_poll(&tty->write_wait, POLLOUT); - wake_up_interruptible_poll(&tty->read_wait, POLLIN); + + wake_up_interruptible_poll(&tty->write_wait, EPOLLOUT); + wake_up_interruptible_poll(&tty->read_wait, EPOLLIN); + /* * Shutdown the current line discipline, and reset it to * N_TTY if need be. * * Avoid racing set_ldisc or tty_ldisc_release */ - mutex_lock(&tty->ldisc_mutex); - - if (tty_ldisc_hangup_halt(tty)) { + tty_ldisc_lock(tty, MAX_SCHEDULE_TIMEOUT); - /* At this point we have a halted ldisc; we want to close it and - reopen a new ldisc. We could defer the reopen to the next - open but it means auditing a lot of other paths so this is - a FIXME */ - if (reset == 0) { - - if (!tty_ldisc_reinit(tty, tty->termios.c_line)) - err = tty_ldisc_open(tty, tty->ldisc); - else - err = 1; - } - /* If the re-open fails or we reset then go to N_TTY. The - N_TTY open cannot fail */ - if (reset || err) { - BUG_ON(tty_ldisc_reinit(tty, N_TTY)); - WARN_ON(tty_ldisc_open(tty, tty->ldisc)); - } - tty_ldisc_enable(tty); - } - mutex_unlock(&tty->ldisc_mutex); - if (reset) + if (tty->driver->flags & TTY_DRIVER_RESET_TERMIOS) tty_reset_termios(tty); - tty_ldisc_debug(tty, "re-opened ldisc: %p\n", tty->ldisc); + if (tty->ldisc) { + if (reinit) { + if (tty_ldisc_reinit(tty, tty->termios.c_line) < 0 && + tty_ldisc_reinit(tty, N_TTY) < 0) + WARN_ON(tty_ldisc_reinit(tty, N_NULL) < 0); + } else + tty_ldisc_kill(tty); + } + tty_ldisc_unlock(tty); } /** - * tty_ldisc_setup - open line discipline - * @tty: tty being shut down - * @o_tty: pair tty for pty/tty pairs + * tty_ldisc_setup - open line discipline + * @tty: tty being shut down + * @o_tty: pair tty for pty/tty pairs * - * Called during the initial open of a tty/pty pair in order to set up the - * line disciplines and bind them to the tty. This has no locking issues - * as the device isn't yet active. + * Called during the initial open of a tty/pty pair in order to set up the line + * disciplines and bind them to the @tty. This has no locking issues as the + * device isn't yet active. */ - int tty_ldisc_setup(struct tty_struct *tty, struct tty_struct *o_tty) { - struct tty_ldisc *ld = tty->ldisc; - int retval; + int retval = tty_ldisc_open(tty, tty->ldisc); - retval = tty_ldisc_open(tty, ld); if (retval) return retval; if (o_tty) { + /* + * Called without o_tty->ldisc_sem held, as o_tty has been + * just allocated and no one has a reference to it. + */ retval = tty_ldisc_open(o_tty, o_tty->ldisc); if (retval) { - tty_ldisc_close(tty, ld); + tty_ldisc_close(tty, tty->ldisc); return retval; } - tty_ldisc_enable(o_tty); } - tty_ldisc_enable(tty); return 0; } -static void tty_ldisc_kill(struct tty_struct *tty) -{ - mutex_lock(&tty->ldisc_mutex); - /* - * Now kill off the ldisc - */ - tty_ldisc_close(tty, tty->ldisc); - tty_ldisc_put(tty->ldisc); - /* Force an oops if we mess this up */ - tty->ldisc = NULL; - - /* Ensure the next open requests the N_TTY ldisc */ - tty_set_termios_ldisc(tty, N_TTY); - mutex_unlock(&tty->ldisc_mutex); -} - /** - * tty_ldisc_release - release line discipline - * @tty: tty being shut down - * @o_tty: pair tty for pty/tty pairs + * tty_ldisc_release - release line discipline + * @tty: tty being shut down (or one end of pty pair) * - * Called during the final close of a tty/pty pair in order to shut down - * the line discpline layer. On exit the ldisc assigned is N_TTY and the - * ldisc has not been opened. + * Called during the final close of a tty or a pty pair in order to shut down + * the line discpline layer. On exit, each tty's ldisc is %NULL. */ - -void tty_ldisc_release(struct tty_struct *tty, struct tty_struct *o_tty) +void tty_ldisc_release(struct tty_struct *tty) { + struct tty_struct *o_tty = tty->link; + /* * Shutdown this line discipline. As this is the final close, * it does not race with the set_ldisc code path. */ - tty_ldisc_debug(tty, "closing ldisc: %p\n", tty->ldisc); - - tty_ldisc_halt(tty, o_tty, MAX_SCHEDULE_TIMEOUT); - - tty_lock_pair(tty, o_tty); - /* This will need doing differently if we need to lock */ + tty_ldisc_lock_pair(tty, o_tty); tty_ldisc_kill(tty); if (o_tty) tty_ldisc_kill(o_tty); + tty_ldisc_unlock_pair(tty, o_tty); - tty_unlock_pair(tty, o_tty); - /* And the memory resources remaining (buffers, termios) will be - disposed of when the kref hits zero */ + /* + * And the memory resources remaining (buffers, termios) will be + * disposed of when the kref hits zero + */ - tty_ldisc_debug(tty, "ldisc closed\n"); + tty_ldisc_debug(tty, "released\n"); } /** - * tty_ldisc_init - ldisc setup for new tty - * @tty: tty being allocated + * tty_ldisc_init - ldisc setup for new tty + * @tty: tty being allocated * - * Set up the line discipline objects for a newly allocated tty. Note that - * the tty structure is not completely set up when this call is made. + * Set up the line discipline objects for a newly allocated tty. Note that the + * tty structure is not completely set up when this call is made. */ - -void tty_ldisc_init(struct tty_struct *tty) +int tty_ldisc_init(struct tty_struct *tty) { - struct tty_ldisc *ld = tty_ldisc_get(N_TTY); + struct tty_ldisc *ld = tty_ldisc_get(tty, N_TTY); + if (IS_ERR(ld)) - panic("n_tty: init_tty"); + return PTR_ERR(ld); tty->ldisc = ld; + return 0; } /** - * tty_ldisc_init - ldisc cleanup for new tty - * @tty: tty that was allocated recently + * tty_ldisc_deinit - ldisc cleanup for new tty + * @tty: tty that was allocated recently * - * The tty structure must not becompletely set up (tty_ldisc_setup) when - * this call is made. + * The tty structure must not be completely set up (tty_ldisc_setup()) when + * this call is made. */ void tty_ldisc_deinit(struct tty_struct *tty) { - tty_ldisc_put(tty->ldisc); + /* no ldisc_sem, tty is being destroyed */ + if (tty->ldisc) + tty_ldisc_put(tty->ldisc); tty->ldisc = NULL; } - -void tty_ldisc_begin(void) -{ - /* Setup the default TTY line discipline. */ - (void) tty_register_ldisc(N_TTY, &tty_ldisc_N_TTY); -} |