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authorChristoph Hellwig <hch@lst.de>2010-05-19 20:53:10 +0200
committerAurelien Jarno <aurelien@aurel32.net>2010-05-27 13:58:34 +0200
commit1fb9798b69d7a2fccce70aebe5c5162cf069d596 (patch)
treeca2e4491f6bc331b4ed40f424c20284521876939
parentpci: irq_state vmstate breakage (diff)
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block: fix sector comparism in multiwrite_req_compare
The difference between the start sectors of two requests can be larger than the size of the "int" type, which can lead to a not correctly sorted multiwrite array and thus spurious I/O errors and filesystem corruption due to incorrect request merges. So instead of doing the cute sector arithmetics trick spell out the exact comparisms. Spotted by Kevin Wolf based on a testcase from Michael Tokarev. Signed-off-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Kevin Wolf <kwolf@redhat.com> (cherry picked from commit 77be4366baface6613cfc312ba281f8e5860997c)
-rw-r--r--block.c14
1 files changed, 13 insertions, 1 deletions
diff --git a/block.c b/block.c
index 7326bfeee..955eeaa7b 100644
--- a/block.c
+++ b/block.c
@@ -1636,7 +1636,19 @@ static void multiwrite_cb(void *opaque, int ret)
static int multiwrite_req_compare(const void *a, const void *b)
{
- return (((BlockRequest*) a)->sector - ((BlockRequest*) b)->sector);
+ const BlockRequest *req1 = a, *req2 = b;
+
+ /*
+ * Note that we can't simply subtract req2->sector from req1->sector
+ * here as that could overflow the return value.
+ */
+ if (req1->sector > req2->sector) {
+ return 1;
+ } else if (req1->sector < req2->sector) {
+ return -1;
+ } else {
+ return 0;
+ }
}
/*