From patchwork Thu Dec 19 19:20:47 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Darrick J. Wong" X-Patchwork-Id: 13915541 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 666321A9B53; Thu, 19 Dec 2024 19:20:48 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1734636048; cv=none; b=adFaQVRVV/7zX9Huq+vJFmq/MEuSxnmlgqMKK+bF0CNK0lEm8C1ZLQ7hGSUKwFbqZDSsKJhdxSShH8hpyzI9lDL6aCZsDJmi+6kHlm3L5j6Bsb8jO2ZgdVMTRMGIgg0iTa6OnfYi/sXPcI+DBPESnJL+BiFFpsPYoXZPBw8NqJ8= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1734636048; c=relaxed/simple; bh=EXnrut/7cp8GX1BFNcfEjeRFFG/TWYFDDVd0rm5b0Uo=; h=Date:Subject:From:To:Cc:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=VRX7fPh9DM/IfIAGJ2FfxGnhbsNUHIIVSLZatYZ2L+H2o62z7kKKpxGOKElVs5Qvh82wXnPg8/2ucl0WcZfZg2Q5I8ScR0pCR2j+MgFIQo3y7DLMc2OsLKALDBd6xiA4bNuoKV870Waa1SVa1t5O4YGWcp0obH11E3oF5ajks5g= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Fsp4U8EW; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="Fsp4U8EW" Received: by smtp.kernel.org (Postfix) with ESMTPSA id F0982C4CECE; Thu, 19 Dec 2024 19:20:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1734636048; bh=EXnrut/7cp8GX1BFNcfEjeRFFG/TWYFDDVd0rm5b0Uo=; h=Date:Subject:From:To:Cc:In-Reply-To:References:From; b=Fsp4U8EW33mjVCVvN40yiFTfX17deOVpKkcjUMD67p3iyXMT2ZTwD3lFaXqYNSBym k2gOIh7F3ppQokWfT9xb+c7x2cKQ97X2+hyO2bmZTluQD1s9HKImfiK75lkl4H5jop Ed3OZ8RcaE5NLDmad/OX1rIBrCsdsrw+y4t5jOf/jpfIU9ekLUmmqfcZpmyxRz+jm3 a6JB6MoPZI/lz0JZSey8a8bciGjztRmmjv7JJGMzHZWMk1cxpGibIOIGEksgeeNtPw yEA0nbWETycllrVzhwwTOcfTgNJbP9Hmqk5ATtJOnIyeI5VkBmPaooXmK/4U/4Fjyx vJJwQmHsj8ttQ== Date: Thu, 19 Dec 2024 11:20:47 -0800 Subject: [PATCH 2/2] xfs: release the dquot buf outside of qli_lock From: "Darrick J. Wong" To: djwong@kernel.org Cc: syzbot+3126ab3db03db42e7a31@syzkaller.appspotmail.com, stable@vger.kernel.org, syzbot+3126ab3db03db42e7a31@syzkaller.appspotmail.com, linux-xfs@vger.kernel.org, hch@lst.de Message-ID: <173463578249.1570935.14851151691186464527.stgit@frogsfrogsfrogs> In-Reply-To: <173463578212.1570935.4004660775026906039.stgit@frogsfrogsfrogs> References: <173463578212.1570935.4004660775026906039.stgit@frogsfrogsfrogs> Precedence: bulk X-Mailing-List: linux-xfs@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 From: Darrick J. Wong Lai Yi reported a lockdep complaint about circular locking: Chain exists of: &lp->qli_lock --> &bch->bc_lock --> &l->lock Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(&l->lock); lock(&bch->bc_lock); lock(&l->lock); lock(&lp->qli_lock); I /think/ the problem here is that xfs_dquot_attach_buf during quotacheck will release the buffer while it's holding the qli_lock. Because this is a cached buffer, xfs_buf_rele_cached takes b_lock before decrementing b_hold. Other threads have taught lockdep that a locking dependency chain is bp->b_lock -> bch->bc_lock -> l(ru)->lock; and that another chain is l(ru)->lock -> lp->qli_lock. Hence we do not want to take b_lock while holding qli_lock. Reported-by: syzbot+3126ab3db03db42e7a31@syzkaller.appspotmail.com Cc: # v6.13-rc3 Fixes: ca378189fdfa89 ("xfs: convert quotacheck to attach dquot buffers") Tested-by: syzbot+3126ab3db03db42e7a31@syzkaller.appspotmail.com Signed-off-by: "Darrick J. Wong" Reviewed-by: Christoph Hellwig --- fs/xfs/xfs_dquot.c | 12 ++++++++---- 1 file changed, 8 insertions(+), 4 deletions(-) diff --git a/fs/xfs/xfs_dquot.c b/fs/xfs/xfs_dquot.c index f11d475898f280..576b7755b1f1fc 100644 --- a/fs/xfs/xfs_dquot.c +++ b/fs/xfs/xfs_dquot.c @@ -1315,7 +1315,8 @@ xfs_dquot_read_buf( /* * Attach a dquot buffer to this dquot to avoid allocating a buffer during a - * dqflush, since dqflush can be called from reclaim context. + * dqflush, since dqflush can be called from reclaim context. Caller must hold + * the dqlock. */ int xfs_dquot_attach_buf( @@ -1336,13 +1337,16 @@ xfs_dquot_attach_buf( return error; /* - * Attach the dquot to the buffer so that the AIL does not have - * to read the dquot buffer to push this item. + * Hold the dquot buffer so that we retain our ref to it after + * detaching it from the transaction, then give that ref to the + * dquot log item so that the AIL does not have to read the + * dquot buffer to push this item. */ xfs_buf_hold(bp); + xfs_trans_brelse(tp, bp); + spin_lock(&qlip->qli_lock); lip->li_buf = bp; - xfs_trans_brelse(tp, bp); } qlip->qli_dirty = true; spin_unlock(&qlip->qli_lock);