On Friday, April 29, 2011, Tejun Heo wrote: > From 5035b20fa5cd146b66f5f89619c20a4177fb736d Mon Sep 17 00:00:00 2001 > From: Tejun Heo <tj@xxxxxxxxxx> > Date: Fri, 29 Apr 2011 18:08:37 +0200 > > If a rescuer and stop_machine() bringing down a CPU race with each > other, they may deadlock on non-preemptive kernel. The CPU won't > accept a new task, so the rescuer can't migrate to the target CPU, > while stop_machine() can't proceed because the rescuer is holding one > of the CPU retrying migration. GCWQ_DISASSOCIATED is never cleared > and worker_maybe_bind_and_lock() retries indefinitely. > > This problem can be reproduced semi reliably while the system is > entering suspend. > > http://thread.gmane.org/gmane.linux.kernel/1122051 > > A lot of kudos to Thilo-Alexander for reporting this tricky issue and > painstaking testing. > > stable: This affects all kernels with cmwq, so all kernels since and > including v2.6.36 need this fix. Well, _that_ explains quite a number of mysterious reports where suspend or poweroff hang randomly. Thanks a lot of fixing it! Rafael > Signed-off-by: Tejun Heo <tj@xxxxxxxxxx> > Reported-by: Thilo-Alexander Ginkel <thilo@xxxxxxxxxx> > Tested-by: Thilo-Alexander Ginkel <thilo@xxxxxxxxxx> > Cc: stable@xxxxxxxxxx > --- > Will soon send pull request to Linus. Thank you very much. > > kernel/workqueue.c | 8 +++++++- > 1 files changed, 7 insertions(+), 1 deletions(-) > > diff --git a/kernel/workqueue.c b/kernel/workqueue.c > index 04ef830..e3378e8 100644 > --- a/kernel/workqueue.c > +++ b/kernel/workqueue.c > @@ -1291,8 +1291,14 @@ __acquires(&gcwq->lock) > return true; > spin_unlock_irq(&gcwq->lock); > > - /* CPU has come up inbetween, retry migration */ > + /* > + * We've raced with CPU hot[un]plug. Give it a breather > + * and retry migration. cond_resched() is required here; > + * otherwise, we might deadlock against cpu_stop trying to > + * bring down the CPU on non-preemptive kernel. > + */ > cpu_relax(); > + cond_resched(); > } > } > > -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
