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authorTejun Heo <tj@kernel.org>2016-01-15 16:58:24 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2016-01-16 11:17:25 -0800
commit8d91f8b15361dfb438ab6eb3b319e2ded43458ff (patch)
tree2462bccec78ae730a5e0801dbb636cb0710a6c88 /include/linux/console.h
parent81cc26f2bd11ba4421a17a2d5cebe4bba206c239 (diff)
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printk: do cond_resched() between lines while outputting to consoles
@console_may_schedule tracks whether console_sem was acquired through lock or trylock. If the former, we're inside a sleepable context and console_conditional_schedule() performs cond_resched(). This allows console drivers which use console_lock for synchronization to yield while performing time-consuming operations such as scrolling. However, the actual console outputting is performed while holding irq-safe logbuf_lock, so console_unlock() clears @console_may_schedule before starting outputting lines. Also, only a few drivers call console_conditional_schedule() to begin with. This means that when a lot of lines need to be output by console_unlock(), for example on a console registration, the task doing console_unlock() may not yield for a long time on a non-preemptible kernel. If this happens with a slow console devices, for example a serial console, the outputting task may occupy the cpu for a very long time. Long enough to trigger softlockup and/or RCU stall warnings, which in turn pile more messages, sometimes enough to trigger the next cycle of warnings incapacitating the system. Fix it by making console_unlock() insert cond_resched() between lines if @console_may_schedule. Signed-off-by: Tejun Heo <tj@kernel.org> Reported-by: Calvin Owens <calvinowens@fb.com> Acked-by: Jan Kara <jack@suse.com> Cc: Dave Jones <davej@codemonkey.org.uk> Cc: Kyle McMartin <kyle@kernel.org> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'include/linux/console.h')
-rw-r--r--include/linux/console.h1
1 files changed, 1 insertions, 0 deletions
diff --git a/include/linux/console.h b/include/linux/console.h
index bd194343c346..ea731af2451e 100644
--- a/include/linux/console.h
+++ b/include/linux/console.h
@@ -150,6 +150,7 @@ extern int console_trylock(void);
extern void console_unlock(void);
extern void console_conditional_schedule(void);
extern void console_unblank(void);
+extern void console_flush_on_panic(void);
extern struct tty_driver *console_device(int *);
extern void console_stop(struct console *);
extern void console_start(struct console *);