Re: [PATCH] md: do not use ++ in rcu_dereference() argument
From: Sam Ravnborg <hidden>
Date: 2010-09-05 19:01:43
Also in:
kernel-janitors, lkml
On Sun, Sep 05, 2010 at 10:32:18PM +0400, Kulikov Vasiliy wrote:
quoted hunk ↗ jump to hunk
From: Vasiliy Kulikov <redacted> rcu_dereference() is macro, so it might use its argument twice. Argument must not has side effects. It was found by compiler warning: drivers/md/raid1.c: In function ‘read_balance’: drivers/md/raid1.c:445: warning: operation on ‘new_disk’ may be undefined Signed-off-by: Vasiliy Kulikov <redacted> --- drivers/md/raid1.c | 3 ++- 1 files changed, 2 insertions(+), 1 deletions(-)diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c index ad83a4d..12194df 100644 --- a/drivers/md/raid1.c +++ b/drivers/md/raid1.c@@ -442,7 +442,7 @@ static int read_balance(conf_t *conf, r1bio_t *r1_bio) r1_bio->bios[new_disk] == IO_BLOCKED || !rdev || !test_bit(In_sync, &rdev->flags) || test_bit(WriteMostly, &rdev->flags); - rdev = rcu_dereference(conf->mirrors[++new_disk].rdev)) { + rdev = rcu_dereference(conf->mirrors[new_disk].rdev)) { if (rdev && test_bit(In_sync, &rdev->flags) && r1_bio->bios[new_disk] != IO_BLOCKED)@@ -452,6 +452,7 @@ static int read_balance(conf_t *conf, r1bio_t *r1_bio) new_disk = wonly_disk; break; } + new_disk++; } goto rb_out;
This change looks wrong. In the original implementation new_disk is incremented and then we do the array lookup. With your implementation it looks like we increment it after the array lookup. Sam -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html