Date: Wed, 31 Jul 2019 02:12:56 +0300 From: Konstantin Belousov <kostikbel@gmail.com> To: Bryan Drewery <bdrewery@FreeBSD.org> Cc: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: Re: svn commit: r350005 - head/sys/kern Message-ID: <20190730231256.GL2731@kib.kiev.ua> In-Reply-To: <d281e1dc-1931-20a5-9f41-7c1f66d4f667@FreeBSD.org> References: <201907151918.x6FJIPFo077975@repo.freebsd.org> <d281e1dc-1931-20a5-9f41-7c1f66d4f667@FreeBSD.org>
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On Tue, Jul 30, 2019 at 03:04:57PM -0700, Bryan Drewery wrote: > On 7/15/2019 12:18 PM, Konstantin Belousov wrote: > > Author: kib > > Date: Mon Jul 15 19:18:25 2019 > > New Revision: 350005 > > URL: https://svnweb.freebsd.org/changeset/base/350005 > > > > Log: > > In do_sem2_wait(), balance umtx_key_get() with umtx_key_release() on retry. > > > > Is this also needed in do_sem_wait()? A similar pattern seems to be there. No, I do not think do_sem_wait() has similar issue, because the again label does not re-get the key. > > I ask because of what I referenced on IRC. I have some processes stuck > in here from a 10.4 jail. > > > ~/git/poudriere # procstat -kk 1498 > > PID TID COMM TDNAME KSTACK > > 1498 100710 python2.7 - mi_switch+0x174 sleepq_switch+0x110 sleepq_catch_signals+0x417 sleepq_wait_sig+0xf _sleep+0x2d0 umtxq_sleep+0x153 do_sem_wait+0x42c __umtx_op_sem_wait+0x6e amd64_syscall+0x2bb fast_syscall_common+0x101 > > 1498 101575 python2.7 - mi_switch+0x174 sleepq_switch+0x110 sleepq_catch_signals+0x417 sleepq_wait_sig+0xf _sleep+0x2d0 umtxq_sleep+0x153 do_sem_wait+0x42c __umtx_op_sem_wait+0x6e amd64_syscall+0x2bb fast_syscall_common+0x101 > > 1498 101657 python2.7 - <running> > ... > > ~/git/poudriere # procstat -kk 1498 > > PID TID COMM TDNAME KSTACK > > 1498 100710 python2.7 - mi_switch+0x174 sleepq_switch+0x110 sleepq_catch_signals+0x417 sleepq_wait_sig+0xf _sleep+0x2d0 umtxq_sleep+0x153 do_sem_wait+0x42c __umtx_op_sem_wait+0x6e amd64_syscall+0x2bb fast_syscall_common+0x101 > > 1498 101575 python2.7 - mi_switch+0x174 sleepq_switch+0x110 sleepq_catch_signals+0x417 sleepq_wait_sig+0xf _sleep+0x2d0 umtxq_sleep+0x153 do_sem_wait+0x42c __umtx_op_sem_wait+0x6e amd64_syscall+0x2bb fast_syscall_common+0x101 > > 1498 101657 python2.7 - do_sem_wait+0x1b6 __umtx_op_sem_wait+0x6e amd64_syscall+0x2bb fast_syscall_common+0x101 > ... > > ~/git/poudriere # procstat -kk 94392 > > PID TID COMM TDNAME KSTACK > > 94392 101815 python2.7 - mi_switch+0x174 sleepq_switch+0x110 sleepq_catch_signals+0x417 sleepq_wait_sig+0xf _sleep+0x2d0 umtxq_sleep+0x153 do_sem_wait+0x42c __umtx_op_sem_wait+0x6e amd64_syscall+0x2bb fast_syscall_common+0x101 > > 94392 101816 python2.7 - __mtx_lock_sleep+0x118 __mtx_lock_flags+0x102 _sleep+0x334 umtxq_busy+0xb7 do_sem_wait+0x161 __umtx_op_sem_wait+0x6e amd64_syscall+0x2bb fast_syscall_common+0x101 > > 94392 102076 python2.7 - __mtx_lock_flags+0x94 do_sem_wait+0x228 __umtx_op_sem_wait+0x6e amd64_syscall+0x2bb fast_syscall_common+0x101 Try this. We should only retry casueword if it failed spuriously. diff --git a/sys/kern/kern_umtx.c b/sys/kern/kern_umtx.c index bb998457975..6c914ab6f3e 100644 --- a/sys/kern/kern_umtx.c +++ b/sys/kern/kern_umtx.c @@ -3229,7 +3229,8 @@ do_sem_wait(struct thread *td, struct _usem *sem, struct _umtx_time *timeout) rv = casueword32(&sem->_has_waiters, 0, &count1, 1); if (rv == 0) rv1 = fueword32(&sem->_count, &count); - if (rv == -1 || (rv == 0 && (rv1 == -1 || count != 0)) || rv == 1) { + if (rv == -1 || (rv == 0 && (rv1 == -1 || count != 0)) || + (rv == 1 && count1 == 0)) { umtxq_lock(&uq->uq_key); umtxq_unbusy(&uq->uq_key); umtxq_remove(uq);
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