Subject: + printk-enable-interrupts-before-calling-console_trylock_for_printk.patch added to -mm tree
To: jack@xxxxxxx
From: akpm@xxxxxxxxxxxxxxxxxxxx
Date: Wed, 23 Apr 2014 13:58:52 -0700
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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------------------------------------------------------
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()
especially since later in the patch series we will want to spin on
console_sem in console_trylock_for_printk().
Signed-off-by: Jan Kara <jack@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
kernel/printk/printk.c | 29 ++++++++++++++++++-----------
1 file changed, 18 insertions(+), 11 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
@@ -1394,10 +1394,9 @@ 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)
{
@@ -1410,8 +1409,10 @@ 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;
/*
@@ -1581,7 +1582,8 @@ 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();
}
@@ -1684,17 +1686,22 @@ asmlinkage int vprintk_emit(int facility
logbuf_cpu = UINT_MAX;
raw_spin_unlock(&logbuf_lock);
+ lockdep_on();
+ local_irq_restore(flags);
+
+ /*
+ * 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();
-
- lockdep_on();
-out_restore_irqs:
- local_irq_restore(flags);
+ preempt_enable();
return printed_len;
}
_
Patches currently in -mm which might be from jack@xxxxxxx are
origin.patch
fanotify-fan_mark_flush-avoid-having-to-provide-a-fake-invalid-fd-and-path.patch
fanotify-create-fan_access-event-for-readdir.patch
fs-notify-markc-trivial-cleanup.patch
fs-mpagec-forgotten-write_sync-in-case-of-data-integrity-write.patch
printk-split-code-for-making-free-space-in-the-log-buffer.patch
printk-ignore-too-long-messages.patch
printk-split-message-size-computation.patch
printk-shrink-too-long-messages.patch
printk-return-really-stored-message-length.patch
printk-remove-outdated-comment.patch
printk-release-lockbuf_lock-before-calling-console_trylock_for_printk.patch
printk-release-lockbuf_lock-before-calling-console_trylock_for_printk-fix.patch
printk-enable-interrupts-before-calling-console_trylock_for_printk.patch
printk-remove-separate-printk_sched-buffers-and-use-printk-buf-instead.patch
linux-next.patch
mm-add-strictlimit-knob-v2.patch
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