On 11/28/2013 02:26 PM, Peter Zijlstra wrote:
Subject: sched: Remove PREEMPT_NEED_RESCHED from generic code
While hunting a preemption issue with Alexander, Ben noticed that the
currently generic PREEMPT_NEED_RESCHED stuff is horribly broken for
load-store architectures.
We currently rely on the IPI to fold TIF_NEED_RESCHED into
PREEMPT_NEED_RESCHED, but when this IPI lands while we already have
a load for the preempt-count but before the store, the store will erase
the PREEMPT_NEED_RESCHED change.
The current preempt-count only works on load-store archs because
interrupts are assumed to be completely balanced wrt their preempt_count
fiddling; the previous preempt_count load will match the preempt_count
state after the interrupt and therefore nothing gets lost.
This patch removes the PREEMPT_NEED_RESCHED usage from generic code and
pushes it into x86 arch code; the generic code goes back to relying on
TIF_NEED_RESCHED.
Boot tested on x86_64 and compile tested on ppc64.
Reported-by: Alexander Graf <ag...@suse.de>
Reported-by: Benjamin Herrenschmidt <b...@kernel.crashing.org>
Signed-off-by: Peter Zijlstra <pet...@infradead.org>
Fixes the issue for me.
Tested-by: Alexander Graf <ag...@suse.de>
Alex
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