The patch titled
Subject: printk: enable interrupts before calling console_trylock_for_printk()
has been added to the -mm tree. Its filename is
printk-enable-interrupts-before-calling-console_trylock_for_printk.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/printk-enable-interrupts-before-calling-console_trylock_for_printk.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/printk-enable-interrupts-before-calling-console_trylock_for_printk.patch
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*** Remember to use Documentation/SubmitChecklist when testing your code ***
The -mm tree is included into linux-next and is updated
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------------------------------------------------------
From: Jan Kara <jack@xxxxxxx>
Subject: 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@xxxxxxx>
Tested-by: Andreas Bombe <aeb@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
kernel/printk/printk.c | 31 +++++++++++++++++++++----------
1 file changed, 21 insertions(+), 10 deletions(-)
diff -puN kernel/printk/printk.c~printk-enable-interrupts-before-calling-console_trylock_for_printk kernel/printk/printk.c
--- a/kernel/printk/printk.c~printk-enable-interrupts-before-calling-console_trylock_for_printk
+++ a/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(unsign
* 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
*/
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
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);
_
Patches currently in -mm which might be from jack@xxxxxxx are
fs-ext4-fsyncc-generic_file_fsync-call-based-on-barrier-flag.patch
fs-mpagec-forgotten-write_sync-in-case-of-data-integrity-write.patch
printk-make-dynamic-kernel-ring-buffer-alignment-explicit.patch
printk-move-power-of-2-practice-of-ring-buffer-size-to-a-helper.patch
printk-make-dynamic-units-clear-for-the-kernel-ring-buffer.patch
printk-allow-increasing-the-ring-buffer-depending-on-the-number-of-cpus.patch
printk-tweak-do_syslog-to-match-comments.patch
printk-rename-default_message_loglevel.patch
printk-fix-some-comments.patch
printk-use-a-clever-macro.patch
printk-miscellaneous-cleanups.patch
printk-enable-interrupts-before-calling-console_trylock_for_printk.patch
fs-isofs-logging-clean-up.patch
linux-next.patch
mm-add-strictlimit-knob-v2.patch
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