From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 3A287434E21; Tue, 15 Sep 2026 04:31:12 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789446684; cv=none; b=LYmnvO5WSj1M9s6hWyQRWwQVdho7Ww86RO918k86k0Z4WCv7JtPmQvBJKEBVXUHgBWhKHA7rKB3bBE+QYek0d3ejSn+oJ0YxkTWP5QX2DPrqjRhg2g5TR8U6FhuQ6WCOj8pAizqucJIP+DPUD7ZnlnH0TzHZXLinwmqBZ8cNfnc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789446684; c=relaxed/simple; bh=mLTNFuKW9fsHo1e2o7AXzHKBwIZje5RsD9hRbi+i/YY=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=Og4H85CQw+4gEFvZ+rLNKCv1ihpT6HRhUby5Vv/6Pt/APXBTAMtcaDIRzrSPosjtkGJwB2WoZnBJlwiDnro6XMzEz4dtO4Zd94WyxgHFiaeJD4hnXcR95J1/PceibgDmYkYfA89wX3E4cFVqBkc81/rcC4eUSHXPhGe3cpt8NrQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=a1iP19UE; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="a1iP19UE" Received: by smtp.kernel.org (Postfix) with UTF8SMTPSA id 175711F000FF; Tue, 15 Sep 2026 04:31:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1789446666; bh=SvOrkac5XCpY8FwPLhGfa51jU5G2Yh36zDzvPoh/hNs=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=a1iP19UE8+gH0RaoGxZKxDGjQazLf6mYbG2THq9kYmJhNcWlIPa/tQcOBqb8MJSq3 4WHQyQZxrycmeVrt6gCt14j6xNa+5N89X4bcDE14r+k7iLDDzEHEfEp5EExhl70g8F UjQyT6VjkqrPJzwhRh7fZVE1XitT3Qa0XHbjD8Wu9xVl6H261GyGu6CqUBoqMdzCxB WAnY1PQng9FBKnqdPV9ws+VE4HSqESdvakKj3o+NszDAVwb70KjL/R8aVHvVrYumRQ a1HcNg4DGQFDgHDPtZkQAig0Ut/bO5OLiEteYRz5Jevg8Ed7IimuPx2N6khiVyTyAQ 8LkeE2lBSzSiQ== Date: Mon, 14 Sep 2026 21:31:05 -0700 From: "Darrick J. Wong" To: "Zhou, Yun" Cc: cem@kernel.org, linux-xfs@vger.kernel.org, linux-kernel@vger.kernel.org, Andrey Albershteyn Subject: Re: [PATCH v3] xfs: don't hold buffer locks across sync transaction commit in xfs_sync_sb_buf Message-ID: <20260915043105.GB2705364@frogsfrogsfrogs> References: <20260731031010.2627884-1-yun.zhou@windriver.com> <20260911174247.GK6265@frogsfrogsfrogs> <4ff8e91e-a5b2-4754-ac9a-20f64f169af0@windriver.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <4ff8e91e-a5b2-4754-ac9a-20f64f169af0@windriver.com> [add xfsprogs maintainer to cc] On Tue, Sep 15, 2026 at 11:18:47AM +0800, Zhou, Yun wrote: > > > On 9/12/26 01:42, Darrick J. Wong wrote: > > CAUTION: This email comes from a non Wind River email account! > > Do not click links or open attachments unless you recognize the sender and know the content is safe. > > > > On Fri, Jul 31, 2026 at 11:10:10AM +0800, Yun Zhou wrote: > > > xfs_sync_sb_buf() holds sb/rtsb buffer locks across a synchronous > > > xfs_trans_commit(), which flushes the CIL push workqueue internally. > > > If shutdown occurs during the CIL push, xfs_buf_item_unpin() needs to > > > lock these buffers to fail them, causing a deadlock: > > > > > > setlabel: holds buf lock -> flush_workqueue(xfs-cil) > > > CIL push worker: xfs_buf_item_unpin -> xfs_buf_lock(same buf) > > > > > > Remove the xfs_trans_bhold() calls so that commit releases the buffer > > > locks normally. After the sync commit, re-acquire the buffers via > > > mp->m_sb_bp / mp->m_rtsb_bp for the on-disk writeback. > > > > > > Fixes: f7664b31975b ("xfs: implement online get/set fs label") > > > Reported-by: syzbot+837bcd54843dd6262f2f@syzkaller.appspotmail.com > > > Closes: https://syzkaller.appspot.com/bug?extid=837bcd54843dd6262f2f > > > Cc: stable@vger.kernel.org > > > Signed-off-by: Yun Zhou > > > Reviewed-by: Christoph Hellwig > > > --- > > > v3: > > > - Drop xfs_buf_hold/xfs_buf_relse, use lock/unlock directly (Christoph). > > > > > > v2: > > > - Remove the bp variable and pass xfs_trans_getsb(tp) directly to > > > xfs_log_rtsb() to fix compilation warnings when CONFIG_XFS_RT=n. > > > - Convert xfs_log_rtsb() stub from macro to inline function to avoid > > > the need for (void) casting (Christoph). > > > --- > > > fs/xfs/libxfs/xfs_rtgroup.h | 6 +++++- > > > fs/xfs/libxfs/xfs_sb.c | 37 +++++++++++++++++-------------------- > > > 2 files changed, 22 insertions(+), 21 deletions(-) > > > > > > diff --git a/fs/xfs/libxfs/xfs_rtgroup.h b/fs/xfs/libxfs/xfs_rtgroup.h > > > index c0b9f9f2c413..fca2eb74908c 100644 > > > --- a/fs/xfs/libxfs/xfs_rtgroup.h > > > +++ b/fs/xfs/libxfs/xfs_rtgroup.h > > > @@ -359,7 +359,11 @@ static inline int xfs_initialize_rtgroups(struct xfs_mount *mp, > > > # define xfs_rtgroup_unlock(rtg, gf) ((void)0) > > > # define xfs_rtgroup_trans_join(tp, rtg, gf) ((void)0) > > > # define xfs_update_rtsb(bp, sb_bp) ((void)0) > > > -# define xfs_log_rtsb(tp, sb_bp) (NULL) > > > +static inline struct xfs_buf *xfs_log_rtsb(struct xfs_trans *tp, > > > + const struct xfs_buf *sb_bp) > > > +{ > > > + return NULL; > > > +} > > > # define xfs_rtgroup_get_geometry(rtg, rgeo) (-EOPNOTSUPP) > > > #endif /* CONFIG_XFS_RT */ > > > > > > diff --git a/fs/xfs/libxfs/xfs_sb.c b/fs/xfs/libxfs/xfs_sb.c > > > index 47322adb7690..2664728f2d8f 100644 > > > --- a/fs/xfs/libxfs/xfs_sb.c > > > +++ b/fs/xfs/libxfs/xfs_sb.c > > > @@ -1470,36 +1470,33 @@ xfs_sync_sb_buf( > > > bool update_rtsb) > > > { > > > struct xfs_trans *tp; > > > - struct xfs_buf *bp; > > > - struct xfs_buf *rtsb_bp = NULL; > > > int error; > > > > > > error = xfs_trans_alloc(mp, &M_RES(mp)->tr_sb, 0, 0, 0, &tp); > > > if (error) > > > return error; > > > > > > - bp = xfs_trans_getsb(tp); > > > xfs_log_sb(tp); > > > - xfs_trans_bhold(tp, bp); > > > - if (update_rtsb) { > > > - rtsb_bp = xfs_log_rtsb(tp, bp); > > > - if (rtsb_bp) > > > - xfs_trans_bhold(tp, rtsb_bp); > > > - } > > > + if (update_rtsb) > > > + xfs_log_rtsb(tp, xfs_trans_getsb(tp)); > > > xfs_trans_set_sync(tp); > > > error = xfs_trans_commit(tp); > > > if (error) > > > - goto out; > > > - /* > > > - * write out the sb buffer to get the changes to disk > > > - */ > > > - error = xfs_bwrite(bp); > > > - if (!error && rtsb_bp) > > > - error = xfs_bwrite(rtsb_bp); > > > -out: > > > - if (rtsb_bp) > > > - xfs_buf_relse(rtsb_bp); > > > - xfs_buf_relse(bp); > > > + return error; > > > + > > > + /* Re-acquire and write the sb and rtsb to disk. */ > > > + xfs_buf_lock(mp->m_sb_bp); > > > > FYI, this causes porting problems to xfsprogs' libxfs because userspace > > doesn't have m_sb_bp or m_rtsb_bp pointers in struct xfs_mount. It's > > not a big deal to add them, but if anyone ever wants to call > > xfs_sync_sb_buf then we're going to have to figure out when to populate > > those pointers. > > > > You're right — the problem is referencing mp->m_sb_bp / mp->m_rtsb_bp > directly in libxfs. I can avoid that by going back to acquiring the > buffer early via xfs_trans_getsb() / xfs_log_rtsb() (as the original > code did), instead of touching the mount pointers. > > To keep this safe for a userspace caller that may not hold a > mount-level reference to the sb buffer, we can take an explicit > xfs_buf_hold() after getsb so the buffer stays alive across the > commit. Unlike the original xfs_trans_bhold(), xfs_buf_hold() only > takes a reference and does not keep the buffer locked across the > commit, so it doesn't reintroduce the deadlock. > > Alternatively, since xfs_ioc_setlabel() is currently the only caller > and it's kernel-only, we could just move xfs_sync_sb_buf() out of > libxfs into xfs_ioctl.c. Probably safer to do that, since there's no other user of that function, and none in userspace. > Since this is already in for-next, would you prefer an incremental follow-up > patch, or should I resend as v4? It's already been merged, so whatever fix we come up with has to be a new patch. --D > Thanks, > Yun > >