>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. 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(); } } -- 1.7.1 -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
