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[Qemu-devel] [PATCH] block: fix sector comparism in multiwrite_req_compa
From: |
Christoph Hellwig |
Subject: |
[Qemu-devel] [PATCH] block: fix sector comparism in multiwrite_req_compare |
Date: |
Wed, 19 May 2010 20:53:10 +0200 |
User-agent: |
Mutt/1.3.28i |
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 <address@hidden>
Index: qemu/block.c
===================================================================
--- qemu.orig/block.c 2010-05-19 17:08:24.970255636 +0200
+++ qemu/block.c 2010-05-19 17:17:34.227006021 +0200
@@ -1933,7 +1933,19 @@ static void multiwrite_cb(void *opaque,
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;
+ }
}
/*
- [Qemu-devel] [PATCH] block: fix sector comparism in multiwrite_req_compare,
Christoph Hellwig <=
- [Qemu-devel] Re: [PATCH] block: fix sector comparism in multiwrite_req_compare, Michael Tokarev, 2010/05/19
- [Qemu-devel] Re: [PATCH] block: fix sector comparism in multiwrite_req_compare, Christoph Hellwig, 2010/05/19
- [Qemu-devel] Re: [PATCH] block: fix sector comparism in multiwrite_req_compare, Michael Tokarev, 2010/05/19
- Re: [Qemu-devel] Re: [PATCH] block: fix sector comparism in multiwrite_req_compare, Kevin Wolf, 2010/05/19
- Re: [Qemu-devel] Re: [PATCH] block: fix sector comparism in multiwrite_req_compare, Avi Kivity, 2010/05/20
- Re: [Qemu-devel] Re: [PATCH] block: fix sector comparism in multiwrite_req_compare, Kevin Wolf, 2010/05/20
- Re: [Qemu-devel] Re: [PATCH] block: fix sector comparism in multiwrite_req_compare, Avi Kivity, 2010/05/20
[Qemu-devel] Re: [PATCH] block: fix sector comparism in multiwrite_req_compare, Kevin Wolf, 2010/05/20