Tejun Heo 0ba4f4bb1a
printk: do cond_resched() between lines while outputting to consoles ...
commit 8d91f8b15361dfb438ab6eb3b319e2ded43458ff upstream.
@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 >
[ciwillia@brocade.com: adjust context for 3.10.y]
Signed-off-by: Chas Williams <ciwillia@brocade.com>
Signed-off-by: Willy Tarreau <w@1wt.eu>
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Tejun Heo
0ba4f4bb1a