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authorJan Kara <jack@suse.cz>2014-08-06 16:09:10 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2014-08-06 18:01:24 -0700
commit5874af2003b1aaaa053128d655710140e3187226 (patch)
tree35ecb809f6fa117b824880fbf05e4f5d5bed902c /kernel
parent249771b8307e7a91659d8b273f8b70d48c3a7bfc (diff)
printk: enable interrupts before calling console_trylock_for_printk()
We need interrupts disabled when calling console_trylock_for_printk() only so that cpu id we pass to can_use_console() remains valid (for other things console_sem provides all the exclusion we need and deadlocks on console_sem due to interrupts are impossible because we use down_trylock()). However if we are rescheduled, we are guaranteed to run on an online cpu so we can easily just get the cpu id in can_use_console(). We can lose a bit of performance when we enable interrupts in vprintk_emit() and then disable them again in console_unlock() but OTOH it can somewhat reduce interrupt latency caused by console_unlock(). We differ from (reverted) commit 939f04bec1a4 in that we avoid calling console_unlock() from vprintk_emit() with lockdep enabled as that has unveiled quite some bugs leading to system freezes during boot (e.g. https://lkml.org/lkml/2014/5/30/242, https://lkml.org/lkml/2014/6/28/521). Signed-off-by: Jan Kara <jack@suse.cz> Tested-by: Andreas Bombe <aeb@debian.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/printk/printk.c31
1 files changed, 21 insertions, 10 deletions
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 5eb0e6c800bb..df202fe0974a 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -1450,10 +1450,9 @@ static int have_callable_console(void)
/*
* Can we actually use the console at this time on this cpu?
*
- * Console drivers may assume that per-cpu resources have
- * been allocated. So unless they're explicitly marked as
- * being able to cope (CON_ANYTIME) don't call them until
- * this CPU is officially up.
+ * Console drivers may assume that per-cpu resources have been allocated. So
+ * unless they're explicitly marked as being able to cope (CON_ANYTIME) don't
+ * call them until this CPU is officially up.
*/
static inline int can_use_console(unsigned int cpu)
{
@@ -1466,8 +1465,10 @@ static inline int can_use_console(unsigned int cpu)
* console_lock held, and 'console_locked' set) if it
* is successful, false otherwise.
*/
-static int console_trylock_for_printk(unsigned int cpu)
+static int console_trylock_for_printk(void)
{
+ unsigned int cpu = smp_processor_id();
+
if (!console_trylock())
return 0;
/*
@@ -1642,7 +1643,8 @@ asmlinkage int vprintk_emit(int facility, int level,
*/
if (!oops_in_progress && !lockdep_recursing(current)) {
recursion_bug = 1;
- goto out_restore_irqs;
+ local_irq_restore(flags);
+ return 0;
}
zap_locks();
}
@@ -1750,21 +1752,30 @@ asmlinkage int vprintk_emit(int facility, int level,
logbuf_cpu = UINT_MAX;
raw_spin_unlock(&logbuf_lock);
+ lockdep_on();
+ local_irq_restore(flags);
/* If called from the scheduler, we can not call up(). */
if (!in_sched) {
+ lockdep_off();
+ /*
+ * Disable preemption to avoid being preempted while holding
+ * console_sem which would prevent anyone from printing to
+ * console
+ */
+ preempt_disable();
+
/*
* Try to acquire and then immediately release the console
* semaphore. The release will print out buffers and wake up
* /dev/kmsg and syslog() users.
*/
- if (console_trylock_for_printk(this_cpu))
+ if (console_trylock_for_printk())
console_unlock();
+ preempt_enable();
+ lockdep_on();
}
- lockdep_on();
-out_restore_irqs:
- local_irq_restore(flags);
return printed_len;
}
EXPORT_SYMBOL(vprintk_emit);