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authorLinus Torvalds <torvalds@linux-foundation.org>2017-05-03 18:29:28 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2017-05-03 18:29:28 -0700
commit9c35baf6cee9a5745d55de6f9995916dde642517 (patch)
treec447401507ed48c36c08e40f1a508c6d0a5601d6
parentdd23f273d9a765d7f092c1bb0d1cd7aaf668077e (diff)
parentcf39bf58afdaabc0b86f141630fb3fd18190294e (diff)
Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/pmladek/printk
Pull printk updates from Petr Mladek: - There is a situation when early console is not deregistered because the preferred one matches a wrong entry. It caused messages to appear twice. This is the 2nd attempt to fix it. The first one was wrong, see the commit c6c7d83b9c9e ('Revert "console: don't prefer first registered if DT specifies stdout-path"'). The fix is coupled with some small code clean up. Well, the console registration code would deserve a big one. We need to think about it. - Do not lose information about the preemtive context when the console semaphore is re-taken. - Do not block CPU hotplug when someone else is already pushing messages to the console. * 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/pmladek/printk: printk: fix double printing with earlycon printk: rename selected_console -> preferred_console printk: fix name/type/scope of preferred_console var printk: Correctly handle preemption in console_unlock() printk: use console_trylock() in console_cpu_notify()
-rw-r--r--kernel/printk/printk.c81
1 files changed, 56 insertions, 25 deletions
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 2984fb0f0257..779479ac9f57 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -269,8 +269,8 @@ static struct console *exclusive_console;
#define MAX_CMDLINECONSOLES 8
static struct console_cmdline console_cmdline[MAX_CMDLINECONSOLES];
+static int console_cmdline_cnt;
-static int selected_console = -1;
static int preferred_console = -1;
int console_set_on_cmdline;
EXPORT_SYMBOL(console_set_on_cmdline);
@@ -1906,24 +1906,38 @@ static int __add_preferred_console(char *name, int idx, char *options,
* See if this tty is not yet registered, and
* if we have a slot free.
*/
- for (i = 0, c = console_cmdline;
- i < MAX_CMDLINECONSOLES && c->name[0];
- i++, c++) {
+ for (i = 0, c = console_cmdline; i < console_cmdline_cnt; i++, c++) {
if (strcmp(c->name, name) == 0 && c->index == idx) {
- if (!brl_options)
- selected_console = i;
+ if (brl_options)
+ return 0;
+
+ /*
+ * Maintain an invariant that will help to find if
+ * the matching console is preferred, see
+ * register_console():
+ *
+ * The last non-braille console is always
+ * the preferred one.
+ */
+ if (i != console_cmdline_cnt - 1)
+ swap(console_cmdline[i],
+ console_cmdline[console_cmdline_cnt - 1]);
+
+ preferred_console = console_cmdline_cnt - 1;
+
return 0;
}
}
if (i == MAX_CMDLINECONSOLES)
return -E2BIG;
if (!brl_options)
- selected_console = i;
+ preferred_console = i;
strlcpy(c->name, name, sizeof(c->name));
c->options = options;
braille_set_options(c, brl_options);
c->index = idx;
+ console_cmdline_cnt++;
return 0;
}
/*
@@ -2031,15 +2045,16 @@ void resume_console(void)
* @cpu: unused
*
* If printk() is called from a CPU that is not online yet, the messages
- * will be spooled but will not show up on the console. This function is
- * called when a new CPU comes online (or fails to come up), and ensures
- * that any such output gets printed.
+ * will be printed on the console only if there are CON_ANYTIME consoles.
+ * This function is called when a new CPU comes online (or fails to come
+ * up) or goes offline.
*/
static int console_cpu_notify(unsigned int cpu)
{
if (!cpuhp_tasks_frozen) {
- console_lock();
- console_unlock();
+ /* If trylock fails, someone else is doing the printing */
+ if (console_trylock())
+ console_unlock();
}
return 0;
}
@@ -2161,7 +2176,7 @@ void console_unlock(void)
}
/*
- * Console drivers are called under logbuf_lock, so
+ * Console drivers are called with interrupts disabled, so
* @console_may_schedule should be cleared before; however, we may
* end up dumping a lot of lines, for example, if called from
* console registration path, and should invoke cond_resched()
@@ -2169,11 +2184,15 @@ void console_unlock(void)
* scheduling stall on a slow console leading to RCU stall and
* softlockup warnings which exacerbate the issue with more
* messages practically incapacitating the system.
+ *
+ * console_trylock() is not able to detect the preemptive
+ * context reliably. Therefore the value must be stored before
+ * and cleared after the the "again" goto label.
*/
do_cond_resched = console_may_schedule;
+again:
console_may_schedule = 0;
-again:
/*
* We released the console_sem lock, so we need to recheck if
* cpu is online and (if not) is there at least one CON_ANYTIME
@@ -2409,6 +2428,7 @@ void register_console(struct console *newcon)
unsigned long flags;
struct console *bcon = NULL;
struct console_cmdline *c;
+ static bool has_preferred;
if (console_drivers)
for_each_console(bcon)
@@ -2435,15 +2455,15 @@ void register_console(struct console *newcon)
if (console_drivers && console_drivers->flags & CON_BOOT)
bcon = console_drivers;
- if (preferred_console < 0 || bcon || !console_drivers)
- preferred_console = selected_console;
+ if (!has_preferred || bcon || !console_drivers)
+ has_preferred = preferred_console >= 0;
/*
* See if we want to use this console driver. If we
* didn't select a console we take the first one
* that registers here.
*/
- if (preferred_console < 0) {
+ if (!has_preferred) {
if (newcon->index < 0)
newcon->index = 0;
if (newcon->setup == NULL ||
@@ -2451,18 +2471,29 @@ void register_console(struct console *newcon)
newcon->flags |= CON_ENABLED;
if (newcon->device) {
newcon->flags |= CON_CONSDEV;
- preferred_console = 0;
+ has_preferred = true;
}
}
}
/*
- * See if this console matches one we selected on
- * the command line.
+ * See if this console matches one we selected on the command line.
+ *
+ * There may be several entries in the console_cmdline array matching
+ * with the same console, one with newcon->match(), another by
+ * name/index:
+ *
+ * pl011,mmio,0x87e024000000,115200 -- added from SPCR
+ * ttyAMA0 -- added from command line
+ *
+ * Traverse the console_cmdline array in reverse order to be
+ * sure that if this console is preferred then it will be the first
+ * matching entry. We use the invariant that is maintained in
+ * __add_preferred_console().
*/
- for (i = 0, c = console_cmdline;
- i < MAX_CMDLINECONSOLES && c->name[0];
- i++, c++) {
+ for (i = console_cmdline_cnt - 1; i >= 0; i--) {
+ c = console_cmdline + i;
+
if (!newcon->match ||
newcon->match(newcon, c->name, c->index, c->options) != 0) {
/* default matching */
@@ -2484,9 +2515,9 @@ void register_console(struct console *newcon)
}
newcon->flags |= CON_ENABLED;
- if (i == selected_console) {
+ if (i == preferred_console) {
newcon->flags |= CON_CONSDEV;
- preferred_console = selected_console;
+ has_preferred = true;
}
break;
}