Messages in this thread | | | From | Sergey Senozhatsky <> | Subject | [RFC][PATCH v3 0/4] let printk()/console_trylock() callers to cond_resched() | Date | Sat, 23 Jan 2016 17:15:09 +0900 |
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[was: cond_resched() some of console_trylock callers]
Hello,
console_unlock() allows to cond_resched() if its caller has set `console_may_schedule' to 1 (this functionality present since commit 'printk: do cond_resched() between lines while outputting to consoles').
The rules are: -- console_lock() always sets `console_may_schedule' to 1 -- console_trylock() always sets `console_may_schedule' to 0
printk() calls console_unlock() with preemption desabled, which basically can lead to RCU stalls, watchdog soft lockups, etc. if something is simultaneously calling printk() frequent enough (IOW, console_sem owner always has new data to send to console divers and can't leave console_unlock() for a long time).
printk()->console_trylock() callers do not necessarily execute in atomic contexts, and some of them can cond_resched() in console_unlock(). console_trylock() can set `console_may_schedule' to 1 (allow cond_resched() later in consoe_unlock()) when it's safe.
0001 addresses a theoretical loss of printk messages. 0002 is an optional optimization patch 0003 drops console_trylock_for_printk 0004 lets some of printk()/console_trylock() callers to cond_resched() in console_unlock()
v2-v3 (thanks to Petr Mladek for reviews): -- do not call can_use_console() on every iteration in console_unlock() (Petr Mladek) -- move "This stops the holder of console_sem.." comment (noted by Petr Mladek) -- take extra care of !PREEMPT_COUNT kernels (Petr Mladek) -- call_console_drivers() still must check cpu_online && CON_ANYTIME (Petr Mladek) -- removed console_trylock_for_printk() (noted by Petr Mladek)
v1-v2: -- make have_callable_console() available for !PRINTK configs (lkp@intel.com) -- take care of RCU preempt kernels in console_trylock()
Sergey Senozhatsky (4): printk: move can_use_console out of console_trylock_for_printk printk: do not console_cont_flush() on every jump to again printk: remove console_trylock_for_printk printk: set may_schedule for some of console_trylock callers
kernel/printk/printk.c | 121 ++++++++++++++++++++++--------------------------- 1 file changed, 55 insertions(+), 66 deletions(-)
-- 2.7.0
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