Messages in this thread |  | | Date | Thu, 12 Dec 2013 14:05:15 -0500 | From | Sasha Levin <> | Subject | Re: [RFC][PATCH 3/5] timekeeping: Avoid possible deadlock from clock_was_set_delayed |
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On 12/12/2013 01:59 PM, John Stultz wrote: > On 12/12/2013 10:32 AM, Sasha Levin wrote: >> On 12/12/2013 11:34 AM, Sasha Levin wrote: >>> On 12/11/2013 02:11 PM, John Stultz wrote: >>>> As part of normal operaions, the hrtimer subsystem frequently calls >>>> into the timekeeping code, creating a locking order of >>>> hrtimer locks -> timekeeping locks >>>> >>>> clock_was_set_delayed() was suppoed to allow us to avoid deadlocks >>>> between the timekeeping the hrtimer subsystem, so that we could >>>> notify the hrtimer subsytem the time had changed while holding >>>> the timekeeping locks. This was done by scheduling delayed work >>>> that would run later once we were out of the timekeeing code. >>>> >>>> But unfortunately the lock chains are complex enoguh that in >>>> scheduling delayed work, we end up eventually trying to grab >>>> an hrtimer lock. >>>> >>>> Sasha Levin noticed this in testing when the new seqlock lockdep >>>> enablement triggered the following (somewhat abrieviated) message: >>> >>> [snip] >>> >>> This seems to work for me, I don't see the lockdep spew anymore. >>> >>> Tested-by: Sasha Levin <sasha.levin@oracle.com> >> >> I think I spoke too soon. >> >> It took way more time to reproduce than previously, but I got: >> >> >> -> #1 (&(&pool->lock)->rlock){-.-...}: >> [ 1195.578519] [<ffffffff81194803>] validate_chain+0x6c3/0x7b0 >> [ 1195.578519] [<ffffffff81194d9d>] __lock_acquire+0x4ad/0x580 >> [ 1195.578519] [<ffffffff81194ff2>] lock_acquire+0x182/0x1d0 >> [ 1195.578519] [<ffffffff843b0760>] _raw_spin_lock+0x40/0x80 >> [ 1195.578519] [<ffffffff81153e0e>] __queue_work+0x14e/0x3f0 >> [ 1195.578519] [<ffffffff81154168>] queue_work_on+0x98/0x120 >> [ 1195.578519] [<ffffffff81161351>] >> clock_was_set_delayed+0x21/0x30 >> [ 1195.578519] [<ffffffff811c4b41>] do_adjtimex+0x111/0x160 >> [ 1195.578519] [<ffffffff811360e3>] SYSC_adjtimex+0x43/0x80 >> [ 1195.578519] [<ffffffff8113612e>] SyS_adjtimex+0xe/0x10 >> [ 1195.578519] [<ffffffff843baed0>] tracesys+0xdd/0xe2 >> [ 1195.578519] > > Are you sure you have that patch applied? > > With it we shouldn't be calling clock_was_set_delayed() from do_adjtimex().
Hm, It seems that there's a conflict there that wasn't resolved properly. Does this patch depend on anything else that's not currently in -next?
Thanks, Sasha
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