From f40bf5f2fcef9e3123faf09cb33a5b0066e55b2d Mon Sep 17 00:00:00 2001 From: Benjamin Herrenschmidt Date: Fri, 16 Apr 2010 23:20:00 +0200 Subject: mutex: Don't spin when the owner CPU is offline or other weird cases commit 4b402210486c6414fe5fbfd85934a0a22da56b04 upstream. Due to recent load-balancer changes that delay the task migration to the next wakeup, the adaptive mutex spinning ends up in a live lock when the owner's CPU gets offlined because the cpu_online() check lives before the owner running check. This patch changes mutex_spin_on_owner() to return 0 (don't spin) in any case where we aren't sure about the owner struct validity or CPU number, and if the said CPU is offline. There is no point going back & re-evaluate spinning in corner cases like that, let's just go to sleep. Signed-off-by: Benjamin Herrenschmidt Signed-off-by: Peter Zijlstra LKML-Reference: <1271212509.13059.135.camel@pasglop> Signed-off-by: Ingo Molnar Signed-off-by: Greg Kroah-Hartman --- kernel/sched.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/kernel/sched.c b/kernel/sched.c index e8aa03646899..9990074169fa 100644 --- a/kernel/sched.c +++ b/kernel/sched.c @@ -5590,7 +5590,7 @@ int mutex_spin_on_owner(struct mutex *lock, struct thread_info *owner) * the mutex owner just released it and exited. */ if (probe_kernel_address(&owner->cpu, cpu)) - goto out; + return 0; #else cpu = owner->cpu; #endif @@ -5600,14 +5600,14 @@ int mutex_spin_on_owner(struct mutex *lock, struct thread_info *owner) * the cpu field may no longer be valid. */ if (cpu >= nr_cpumask_bits) - goto out; + return 0; /* * We need to validate that we can do a * get_cpu() and that we have the percpu area. */ if (!cpu_online(cpu)) - goto out; + return 0; rq = cpu_rq(cpu); @@ -5626,7 +5626,7 @@ int mutex_spin_on_owner(struct mutex *lock, struct thread_info *owner) cpu_relax(); } -out: + return 1; } #endif -- cgit v1.2.3