Messages in this thread Patch in this message | | | Date | Wed, 15 Feb 2017 01:56:45 +0900 | From | Sergey Senozhatsky <> | Subject | Re: Regression in next with use printk_safe buffers in printk |
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On (02/14/17 17:18), Peter Zijlstra wrote: > On Wed, Feb 15, 2017 at 01:01:40AM +0900, Sergey Senozhatsky wrote: > > > > but I'm a bit confused by rt_b->rt_runtime_lock in this unsafe lock > > scenario (so it's not ABBA, but ABAD) > > > > > lock(hrtimer_bases.lock); > > > lock(&rt_b->rt_runtime_lock); > > > lock(hrtimer_bases.lock); > > > lock(tk_core); > > > > > > > > > Chain exists of: > > > > > > tk_core --> &rt_b->rt_runtime_lock --> hrtimer_bases.lock > > > > > > I'm lacking some knowledge here, sorry. where does the tk_core --> &rt_b->rt_runtime_lock > > come from? > > rt_b->rt_runtime_lock is one of the scheduler locks, since we do > printk() under tk_core, which does semaphore muck, which then includes > the entire scheduler chain of locks.
thanks, Peter.
that crossed my mind, but I kinda assumed that we do printk() from under tk_core using sched fair, and rt_runtime_lock is from sched rt.
so something like below, perhaps. would be helpful if Tony can test it.
(I'll send out this patch 'in a proper way' tomorrow, after some sleep, it's 2am here).
8< ====
From e1755b0bf7f8a0be5fdf4dd7303bf4cd150d9d20 Mon Sep 17 00:00:00 2001 From: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Date: Wed, 15 Feb 2017 01:42:18 +0900 Subject: [PATCH] time/timekeeping_debug: use printk_deferred()
Do not call printk() from tk_debug_account_sleep_time(), because tk_debug_account_sleep_time() is called under tk_core seq lock. It's not safe to call printk() under tk_core, because console_sem invokes scheduled (via wake_up_process()->activate_task()), which, in turn, can call timekeeping code again, for instance, via get_time()->ktime_get(). This may result in infinite loop on tk_core.
Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> --- kernel/time/timekeeping_debug.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/kernel/time/timekeeping_debug.c b/kernel/time/timekeeping_debug.c index ca9fb800336b..b8f7146c3538 100644 --- a/kernel/time/timekeeping_debug.c +++ b/kernel/time/timekeeping_debug.c @@ -75,7 +75,8 @@ void tk_debug_account_sleep_time(struct timespec64 *t) int bin = min(fls(t->tv_sec), NUM_BINS-1); sleep_time_bin[bin]++; - pr_info("Suspended for %lld.%03lu seconds\n", (s64)t->tv_sec, + printk_deferred(KERN_INFO "Suspended for %lld.%03lu seconds\n", + (s64)t->tv_sec, t->tv_nsec / NSEC_PER_MSEC); } -- 2.11.1
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