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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