path: root/Documentation/memory-barriers.txt
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authorThomas Gleixner <tglx@linutronix.de>2007-05-23 13:58:18 -0700
committerLinus Torvalds <torvalds@woody.linux-foundation.org>2007-05-23 20:14:15 -0700
commit98d8256739f2c6c636fa2da359f5949c739ae839 (patch)
treee2f92238779ff3012b47a8dd93d57b86b6949793 /Documentation/memory-barriers.txt
parent40acc095302aee380491df5f58d98945243468ec (diff)
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>
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