From 77be4366baface6613cfc312ba281f8e5860997c Mon Sep 17 00:00:00 2001 From: Christoph Hellwig Date: Wed, 19 May 2010 20:53:10 +0200 Subject: [PATCH] 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 Signed-off-by: Kevin Wolf --- block.c | 14 +++++++++++++- 1 file changed, 13 insertions(+), 1 deletion(-) diff --git a/block.c b/block.c index bfe46e3765..89eece7b7b 100644 --- a/block.c +++ b/block.c @@ -1929,7 +1929,19 @@ 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; + } } /* -- GitLab