Messages in this thread | | | Date | Wed, 3 Feb 2016 12:49:30 +0900 | From | Sergey Senozhatsky <> | Subject | Re: [RFC][PATCH v3 0/4] let printk()/console_trylock() callers to cond_resched() |
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Hello,
On (01/23/16 17:15), Sergey Senozhatsky wrote: > [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').
gentlemen, did you get a chance to look into this?
-ss
> 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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