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authorLinus Torvalds <torvalds@woody.linux-foundation.org>2008-02-19 09:08:49 -0800
committerLinus Torvalds <torvalds@woody.linux-foundation.org>2008-02-19 09:08:49 -0800
commit00e962c5408b9f2d0bebd2308673fe982cb9a5fe (patch)
treebe1095cead2711eb26572e8e68054c6fd0f7f3a2 /scripts
parentaa3f98037ce3bcf850bb41f7530754d27481a792 (diff)
Revert "SLUB: Alternate fast paths using cmpxchg_local"
This reverts commit 1f84260c8ce3b1ce26d4c1d6dedc2f33a3a29c0c, which is suspected to be the reason for some very occasional and hard-to-trigger crashes that usually look related to memory allocation (mostly reported in networking, but since that's generally the most common source of shortlived allocations - and allocations in interrupt contexts - that in itself is not a big clue). See for example http://bugzilla.kernel.org/show_bug.cgi?id=9973 http://lkml.org/lkml/2008/2/19/278 etc. One promising suspicion for what the root cause of bug is (which also explains why it's so hard to trigger in practice) came from Eric Dumazet: "I wonder how SLUB_FASTPATH is supposed to work, since it is affected by a classical ABA problem of lockless algo. cmpxchg_local(&c->freelist, object, object[c->offset]) can succeed, while an interrupt came (on this cpu), and several allocations were done, and one free was performed at the end of this interruption, so 'object' was recycled. c->freelist can then contain the previous value (object), but object[c->offset] was changed by IRQ. We then put back in freelist an already allocated object." but another reason for the revert is simply that everybody agrees that this code was the main suspect just by virtue of the pattern of oopses. Cc: Torsten Kaiser <just.for.lkml@googlemail.com> Cc: Christoph Lameter <clameter@sgi.com> Cc: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca> Cc: Pekka Enberg <penberg@cs.helsinki.fi> Cc: Ingo Molnar <mingo@elte.hu> Cc: Eric Dumazet <dada1@cosmosbay.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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