On Tue, 12 May 2015 15:46:26 -0700 "Paul E. McKenney" <[email protected]> wrote:
> From: Patrick Marlier <[email protected]> > > Signed-off-by: Patrick Marlier <[email protected]> > Signed-off-by: Paul E. McKenney <[email protected]> > --- > drivers/md/bitmap.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/md/bitmap.c b/drivers/md/bitmap.c > index 2bc56e2a3526..32901772e4ee 100644 > --- a/drivers/md/bitmap.c > +++ b/drivers/md/bitmap.c > @@ -181,7 +181,7 @@ static struct md_rdev *next_active_rdev(struct md_rdev > *rdev, struct mddev *mdde > rcu_read_lock(); > if (rdev == NULL) > /* start at the beginning */ > - rdev = list_entry_rcu(&mddev->disks, struct md_rdev, same_set); > + rdev = list_entry_rcu(mddev->disks.next, struct md_rdev, > same_set); Hmm, this changes the semantics. The original code looks nasty, I first thought it was broken, but it seems to work out of sheer luck (or clever hack) > else { > /* release the previous rdev and start from there. */ > rdev_dec_pending(rdev, mddev); What comes after this is: list_for_each_entry_continue_rcu(rdev, &mddev->disks, same_set) { if (rdev->raid_disk >= 0 && Now the original code had: rdev = list_entry_rcu(&mddev->disks, struct md_rdev, same_set); Where &mddev->disks would return the address of the disks field of mddev which is a list head. Then it would get the 'same_set' offset, which is 0, and rdev is pointing to a makeshift md_rdev struct. But it isn't used, as the list_for_each_entry_continue_rcu() has: #define list_for_each_entry_continue_rcu(pos, head, member) \ for (pos = list_entry_rcu(pos->member.next, typeof(*pos), member); \ &pos->member != (head); \ pos = list_entry_rcu(pos->member.next, typeof(*pos), member)) Thus the first use of pos is pos->member.next or: mddev->disks.next But now you converted it to rdev = mddev->disks.next, which means the first use is: pos = mddev->disks.next->next I think you are skipping the first element here. -- Steve -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
