]> pilppa.com Git - linux-2.6-omap-h63xx.git/commit
Prevent going idle with softirq pending
authorThomas Gleixner <tglx@linutronix.de>
Wed, 23 May 2007 20:58:18 +0000 (13:58 -0700)
committerLinus Torvalds <torvalds@woody.linux-foundation.org>
Thu, 24 May 2007 03:14:15 +0000 (20:14 -0700)
commit98d8256739f2c6c636fa2da359f5949c739ae839
treee2f92238779ff3012b47a8dd93d57b86b6949793
parent40acc095302aee380491df5f58d98945243468ec
Prevent going idle with softirq pending

The NOHZ patch contains a check for softirqs pending when a CPU goes idle.
The BUG is unrelated to NOHZ, it just was made visible by the NOHZ patch.
The BUG showed up mainly on P4 / hyperthreading enabled machines which lead
the investigations into the wrong direction in the first place.  The real
cause is in cond_resched_softirq():

cond_resched_softirq() is enabling softirqs without invoking the softirq
daemon when softirqs are pending.  This leads to the warning message in the
NOHZ idle code:

t1 runs softirq disabled code on CPU#0
interrupt happens, softirq is raised, but deferred (softirqs disabled)
t1 calls cond_resched_softirq()
enables softirqs via _local_bh_enable()
calls schedule()
t2 runs
t1 is migrated to CPU#1
t2 is done and invokes idle()
NOHZ detects the pending softirq

Fix: change _local_bh_enable() to local_bh_enable() so the softirq
daemon is invoked.

Thanks to Anant Nitya for debugging this with great patience !

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
kernel/sched.c