On Mon, 6 Sep 2010 12:14:08 +1000
Stephen Rothwell <sfr@xxxxxxxxxxxxxxxx> wrote:
> Hi Paul,
>
> After merging the rcu tree, today's linux-next build
> (powerpc ppc64_defconfig) produced this warning:
>
> drivers/md/raid1.c: In function 'read_balance':
> drivers/md/raid1.c:445: warning: operation on 'new_disk' may be undefined
>
> I am picking on the rcu tree because the line above has not changed since
> 2005. The line is:
>
> for (rdev = rcu_dereference(conf->mirrors[new_disk].rdev);
> 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)) {
>
> Where new_disk is being updated in the parameter to the last
> rcu_dereference.
>
Hi Stephen,
There is a patch in linux-kernel
"PATCH] md: do not use ++ in rcu_dereference() argument"
that addresses this - it is a problem in md: I guess rcu as become more
helpful in finding these problems.
I'll probably fix it a little differently, but I'll have something in my
for-next for tomorrow.
Thanks,
NeilBrown
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