From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from userp2120.oracle.com ([156.151.31.85]:57336 "EHLO userp2120.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752338AbdLKUPr (ORCPT ); Mon, 11 Dec 2017 15:15:47 -0500 Date: Mon, 11 Dec 2017 12:09:46 -0800 From: Liu Bo To: Nikolay Borisov Cc: linux-btrfs@vger.kernel.org Subject: Re: [PATCH] Btrfs: raid56: fix race between merge_bio and rbio_orig_end_io Message-ID: <20171211200945.GA10249@lim.localdomain> Reply-To: bo.li.liu@oracle.com References: <20171208230235.30636-1-bo.li.liu@oracle.com> <233e3f98-5f56-c2b8-1aa3-32ea360fe577@suse.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 In-Reply-To: <233e3f98-5f56-c2b8-1aa3-32ea360fe577@suse.com> Sender: linux-btrfs-owner@vger.kernel.org List-ID: On Sat, Dec 09, 2017 at 03:32:18PM +0200, Nikolay Borisov wrote: > > > On 9.12.2017 01:02, Liu Bo wrote: > > We're not allowed to take any new bios to rbio->bio_list in > > rbio_orig_end_io(), otherwise we may get merged with more bios and > > rbio->bio_list is not empty. > > > > This should only happens in error-out cases, the normal path of > > recover and full stripe write have already set RBIO_RMW_LOCKED_BIT to > > disable merge before doing IO. > > > > Reported-by: Jérôme Carretero > > Signed-off-by: Liu Bo > > --- > > fs/btrfs/raid56.c | 13 ++++++++++++- > > 1 file changed, 12 insertions(+), 1 deletion(-) > > > > diff --git a/fs/btrfs/raid56.c b/fs/btrfs/raid56.c > > index 5aa9d22..127c782 100644 > > --- a/fs/btrfs/raid56.c > > +++ b/fs/btrfs/raid56.c > > @@ -859,12 +859,23 @@ static void free_raid_bio(struct btrfs_raid_bio *rbio) > > */ > > static void rbio_orig_end_io(struct btrfs_raid_bio *rbio, blk_status_t err) > > { > > - struct bio *cur = bio_list_get(&rbio->bio_list); > > + struct bio *cur; > > struct bio *next; > > > > + /* > > + * We're not allowed to take any new bios to rbio->bio_list > > + * from now on, otherwise we may get merged with more bios and > > + * rbio->bio_list is not empty. > > + */ > > + spin_lock(&rbio->bio_list_lock); > > + set_bit(RBIO_RMW_LOCKED_BIT, &rbio->flags); > > + spin_unlock(&rbio->bio_list_lock); > > do we really need the spinlock, bit operations are atomic? > Thanks for the question. Atomicity doesn't really matter here, set_bit() needs to be done in the critical section so that merge_rbio() can do right things if merge_rbio() comes after rbio_orig_end_io(). thanks, -liubo > > + > > if (rbio->generic_bio_cnt) > > btrfs_bio_counter_sub(rbio->fs_info, rbio->generic_bio_cnt); > > > > + cur = bio_list_get(&rbio->bio_list); > > + > > free_raid_bio(rbio); > > > > while (cur) { > >