On Wed, Aug 18, 2021 at 9:44 AM Guoqing Jiang <guoqing.jiang@xxxxxxxxx> wrote:
>
>
>
> On 8/18/21 9:36 AM, Xiao Ni wrote:
> > One warning message is triggered like this:
> > [ 695.110751] =============================
> > [ 695.131439] WARNING: suspicious RCU usage
> > [ 695.151389] 4.18.0-319.el8.x86_64+debug #1 Not tainted
> > [ 695.174413] -----------------------------
> > [ 695.192603] drivers/md/raid10.c:1776 suspicious
> > rcu_dereference_check() usage!
> > [ 695.225107] other info that might help us debug this:
> > [ 695.260940] rcu_scheduler_active = 2, debug_locks = 1
> > [ 695.290157] no locks held by mkfs.xfs/10186.
> >
> > In the first loop of function raid10_handle_discard. It already
> > determines which disk need to handle discard request and add the
> > rdev reference count rdev->nr_pending. So the conf->mirrors will
> > not change until all bios come back from underlayer disks. It
> > doesn't need to use rcu_dereference to get rdev.
> >
> > Fixes: d30588b2731f ('md/raid10: improve raid10 discard request')
> > Signed-off-by: Xiao Ni <xni@xxxxxxxxxx>
> > ---
> > drivers/md/raid10.c | 13 +++++++++----
> > 1 file changed, 9 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
> > index 16977e8..1d3ac76 100644
> > --- a/drivers/md/raid10.c
> > +++ b/drivers/md/raid10.c
> > @@ -1712,6 +1712,10 @@ static int raid10_handle_discard(struct mddev *mddev, struct bio *bio)
> > } else
> > r10_bio->master_bio = (struct bio *)first_r10bio;
> >
> > + /* first select target devices under rcu_lock and
> > + * inc refcount on their rdev. Record them by setting
> > + * bios[x] to bio
> > + */
>
> Nit: the comment style is not correct.
Hi Guoqing
/*
* first select target devices under rcu_lock and
* inc refcount on their rdev. Record them by setting
* bios[x] to bio
*/
It should be like this, right? If so, I'll send v2 and add your ack in
the patch too.
