diff options
| author | Jan Kara <jack@suse.cz> | 2014-08-06 16:09:10 -0700 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2014-08-06 18:01:24 -0700 |
| commit | 5874af2003b1aaaa053128d655710140e3187226 (patch) | |
| tree | 35ecb809f6fa117b824880fbf05e4f5d5bed902c /kernel/printk/printk.c | |
| parent | 249771b8307e7a91659d8b273f8b70d48c3a7bfc (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/printk/printk.c')
| -rw-r--r-- | kernel/printk/printk.c | 31 |
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); |