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authorDavid Gibson <dwg@au1.ibm.com>2006-10-13 14:20:59 +1000
committerJeff Garzik <jeff@garzik.org>2006-10-21 14:34:21 -0400
commit5826cade4341a6298eb10d476dccc5f403ca7ad8 (patch)
treed5977bbf1837558b9065e5529d54cb287d056d85 /ipc/util.h
parentcde49b058474ab3f7ff830283e5b538e8fbeefe5 (diff)
[PATCH] ibmveth: Fix index increment calculation
On Thu, Oct 12, 2006 at 06:22:14PM +1000, David Gibson wrote: > Your recent ibmveth commit, 751ae21c6cd1493e3d0a4935b08fb298b9d89773 > ("fix int rollover panic"), causes a rapid oops on my test machine > (POWER5 LPAR). > > I've bisected it down to that commit, but am still investigating the > cause of the crash itself. Found the problem, I believe: an object lesson in the need for great caution using ++. [...] @@ -213,6 +213,7 @@ static void ibmveth_replenish_buffer_poo } free_index = pool->consumer_index++ % pool->size; + pool->consumer_index = free_index; index = pool->free_map[free_index]; ibmveth_assert(index != IBM_VETH_INVALID_MAP); Since the ++ is used as post-increment, the increment is not included in free_index, and so the added line effectively reverts the increment. The produced_index side has an analagous bug. The following change corrects this: The recent commit 751ae21c6cd1493e3d0a4935b08fb298b9d89773 introduced a bug in the producer/consumer index calculation in the ibmveth driver - incautious use of the post-increment ++ operator resulted in an increment being immediately reverted. This patch corrects the logic. Without this patch, the driver oopses almost immediately after activation on at least some machines. Signed-off-by: David Gibson <dwg@au1.ibm.com> Signed-off-by: Jeff Garzik <jeff@garzik.org>
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