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Message-ID: <53ECD7C8.6040202@redhat.com> Date: Thu, 14 Aug 2014 11:37:44 -0400 From: Rik van Riel <riel@...hat.com> To: Oleg Nesterov <oleg@...hat.com> CC: linux-kernel@...r.kernel.org, Peter Zijlstra <peterz@...radead.org>, Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>, Frank Mayhar <fmayhar@...gle.com>, Frederic Weisbecker <fweisbec@...hat.com>, Andrew Morton <akpm@...ux-foundation.org>, Sanjay Rao <srao@...hat.com>, Larry Woodman <lwoodman@...hat.com> Subject: Re: [PATCH RFC] time,signal: protect resource use statistics with seqlock -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 On 08/14/2014 10:24 AM, Oleg Nesterov wrote: > On 08/13, Rik van Riel wrote: >> >> @@ -862,11 +862,9 @@ void do_sys_times(struct tms *tms) { >> cputime_t tgutime, tgstime, cutime, cstime; >> >> - spin_lock_irq(¤t->sighand->siglock); >> thread_group_cputime_adjusted(current, &tgutime, &tgstime); >> cutime = current->signal->cutime; cstime = >> current->signal->cstime; - >> spin_unlock_irq(¤t->sighand->siglock); > > Ah, wait, there is another problem afaics... Last night I worked on another problem with this code. After propagating the stats from a dying task to the signal struct, we need to make sure that that task's stats are not counted twice. This requires zeroing the stats under the write_seqlock, which was easy enough to add. We cannot rely on any state in the task that was set outside of the write_seqlock... > thread_group_cputime_adjusted()->cputime_adjust() plays with > signal->prev_cputime and thus it needs siglock or stats_lock to > ensure it can't race with itself. Not sure it is safe to simply > take the lock in cputime_adjust(), this should be checked. > > OTOH, do_task_stat() already calls task_cputime_adjusted() lockless > and this looks wrong or I missed something. So perhaps we need a > lock in or around cputime_adjust() anyway. I'll take a look at this. - -- All rights reversed -----BEGIN PGP SIGNATURE----- Version: GnuPG v1 iQEcBAEBAgAGBQJT7NfHAAoJEM553pKExN6DTVIH/RIFVl42fM+cBpiSavSa2s4k B0ykVu/VwFbqoYVo5I5joSl25IpU5Xma3AwMBQHoJ7aY9a8w63iGFMoycKcDWbrY nOyaOTvR92aMdn/GuGwS/XlU83PwIbLEyYWFrvn0CrnBqJw9pHz/sLYsvP/jASem LbUStuWFzqGyasb4lJVZmLQKaIVhy30CM5Y3llTFuc16zyH/YG65tUasG+aR2miA g3CiPOHP/IY0vZ+L3YYlLthLY4acVX/bwImE0vsx9fY+rG4hgj5xF9b0CnbaN41g 62oJ4jkFSH/voNFPjR7I5AnKpSeMsBqW2/l1tHlcaKcNCtkd9nri/HinxXN5bN4= =dfSt -----END PGP SIGNATURE----- -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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