Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]
Groups > linux.kernel > #1369251
| From | Xunlei Pang <xpang@redhat.com> |
|---|---|
| Newsgroups | linux.kernel |
| Subject | Re: [PATCH] sched/deadline/rtmutex: Fix a PI crash for deadline tasks |
| Date | 2016-04-01 14:30 +0200 |
| Message-ID | <rj6n9-4aM-15@gated-at.bofh.it> (permalink) |
| References | <rj57J-3qc-27@gated-at.bofh.it> <rj5AK-3Cg-13@gated-at.bofh.it> |
| Organization | linux.* mail to news gateway |
On 2016/04/01 at 19:38, Peter Zijlstra wrote: > On Fri, Apr 01, 2016 at 07:00:18PM +0800, Xunlei Pang wrote: >> I found a kernel crash while playing with deadline PI rtmutex. >> >> BUG: unable to handle kernel NULL pointer dereference at 0000000000000018 >> IP: [<ffffffff810eeb8f>] rt_mutex_get_top_task+0x1f/0x30 >> PGD 232a75067 PUD 230947067 PMD 0 >> Oops: 0000 [#1] SMP >> CPU: 1 PID: 10994 Comm: a.out Not tainted >> >> Call Trace: >> [<ffffffff810cf8aa>] ? enqueue_task_dl+0x2a/0x320 >> [<ffffffff810b658c>] enqueue_task+0x2c/0x80 >> [<ffffffff810ba763>] activate_task+0x23/0x30 >> [<ffffffff810d0ab5>] pull_dl_task+0x1d5/0x260 >> [<ffffffff810d0be6>] pre_schedule_dl+0x16/0x20 >> [<ffffffff8164e783>] __schedule+0xd3/0x900 >> [<ffffffff8164efd9>] schedule+0x29/0x70 >> [<ffffffff8165035b>] __rt_mutex_slowlock+0x4b/0xc0 >> [<ffffffff81650501>] rt_mutex_slowlock+0xd1/0x190 >> [<ffffffff810eeb33>] rt_mutex_timed_lock+0x53/0x60 >> [<ffffffff810ecbfc>] futex_lock_pi.isra.18+0x28c/0x390 >> [<ffffffff810cfa15>] ? enqueue_task_dl+0x195/0x320 >> [<ffffffff810d0bac>] ? prio_changed_dl+0x6c/0x90 >> [<ffffffff810ed8b0>] do_futex+0x190/0x5b0 >> [<ffffffff810edd50>] SyS_futex+0x80/0x180 >> [<ffffffff8165a089>] system_call_fastpath+0x16/0x1b >> RIP [<ffffffff810eeb8f>] rt_mutex_get_top_task+0x1f/0x30 >> >> This is because rt_mutex_enqueue_pi() and rt_mutex_dequeue_pi() >> are only protected by pi_lock when operating pi waiters, while >> rt_mutex_get_top_task() will access them with rq lock held but >> not holding pi_lock. >> >> It's hard for rt_mutex_get_top_task() to hold pi_lock, so the >> patch ensures rt_mutex_enqueue_pi() and rt_mutex_dequeue_pi() >> lock rq when operating "pi_waiters" and "pi_waiters_leftmost". >> We need this iff lock owner has the deadline priority. > How is this deadline specific, those functions you modify are > deadline/rt agnostic. I checked the code, currently only deadline accesses the pi_waiters/pi_waiters_leftmost without pi_lock held via rt_mutex_get_top_task(), other cases all have pi_lock held. So adding the condition. Regards, Xunlei
Back to linux.kernel | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread
[PATCH] sched/deadline/rtmutex: Fix a PI crash for deadline tasks Xunlei Pang <xlpang@redhat.com> - 2016-04-01 13:10 +0200
Re: [PATCH] sched/deadline/rtmutex: Fix a PI crash for deadline tasks Peter Zijlstra <peterz@infradead.org> - 2016-04-01 13:40 +0200
Re: [PATCH] sched/deadline/rtmutex: Fix a PI crash for deadline tasks Xunlei Pang <xpang@redhat.com> - 2016-04-01 14:30 +0200
Re: [PATCH] sched/deadline/rtmutex: Fix a PI crash for deadline tasks Peter Zijlstra <peterz@infradead.org> - 2016-04-01 15:20 +0200
Re: [PATCH] sched/deadline/rtmutex: Fix a PI crash for deadline tasks Xunlei Pang <xpang@redhat.com> - 2016-04-01 15:40 +0200
Re: [PATCH] sched/deadline/rtmutex: Fix a PI crash for deadline tasks Peter Zijlstra <peterz@infradead.org> - 2016-04-02 00:00 +0200
Re: [PATCH] sched/deadline/rtmutex: Fix a PI crash for deadline tasks Xunlei Pang <xpang@redhat.com> - 2016-04-02 12:30 +0200
csiph-web