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 497FC36B918 for ; Fri, 24 Jul 2026 16:53:36 +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=1784912017; cv=none; b=PWf/ghlO0ikz6ynqe1StlRck3A1KyXvZ39F4w+cm1k8rgBm3NjKQ+Yg9NRKGVuR0uujbB7qpfVyRtL4jwkhTO3Yv4cLZDrK0VHCJFMX5qRZr5n1yDhv55tZtPr334eowGJl2VidX4ysBzTzMsD7apk3r9x0fqvIPFjTcnMZHAto= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784912017; c=relaxed/simple; bh=mccxWg4V+3bcmLaTtr81bZLBqxCWZuZ+MRlIiCqNFf0=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=XqBdPDCYg2u8sVA7jL9lu6h+/LBMAKyCCsyh3WijnF6fcfXzbyc5gB3O6CM2ZbFvuax0qMtxcXokQDrlFNJnzLn1Ft3HIwfYnbmiPJK+wfTu/B+I+PjqFwtOYtg+oNgwxHt6qAIEYedPjbub/ZFJW7OVvmGBrxzpA4N8GNmlr9c= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=mlbVvo5Z; 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="mlbVvo5Z" Received: by smtp.kernel.org (Postfix) with UTF8SMTPSA id E50B91F00A3D; Fri, 24 Jul 2026 16:53:35 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1784912016; bh=foAP2GZP5Z2bbIEGtXOQ1yieX+4rH1NguI/IuQfWIe4=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=mlbVvo5Zzkadkd18+yTXYI3rZEzVi5kFEI0iOQ9aAyB+Lh6/ZQZmmcOfuw63GpjLS 51XStSObAby26dJ56LqWNZQ+LUinlGr135VxF8F8h2tFMzQkG/rXBVfV4YvxuSfP/A IUWSHtjblFs5vN3qJMD0MlCqpn0iXkObSlvXCKKiZ7DqEbTUL4vsPv0Ob1aH3r0GYo R1SZTTFwVYM2lehk+36/cSirIPjiWnLdTQsEhinjffbHOdHdRMtOUwNacA4T7LpTFQ LVhW6+N0DRPce3s4/yek77BK5Dc+QNH6P6IVUOMD6AZkQBS/83E4xe4pIfU+sVgOb5 zDLaHHjNj8dOw== Date: Fri, 24 Jul 2026 09:53:35 -0700 From: "Darrick J. Wong" To: Christoph Hellwig Cc: Carlos Maiolino , linux-xfs@vger.kernel.org Subject: Re: [PATCH 07/12] xfs: use WRITE_ONCE to update b_flags Message-ID: <20260724165335.GU2901224@frogsfrogsfrogs> References: <20260715145147.95654-1-hch@lst.de> <20260715145147.95654-8-hch@lst.de> Precedence: bulk X-Mailing-List: linux-xfs@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260715145147.95654-8-hch@lst.de> On Wed, Jul 15, 2026 at 04:51:00PM +0200, Christoph Hellwig wrote: > Prepare for limited lockless reading of flags by using WRITE_ONCE to > prevent the compiler from doing non-standard read-modify-write > operations. > > Signed-off-by: Christoph Hellwig > --- > fs/xfs/xfs_buf.c | 86 ++++++++++++++++++++++++++++-------------------- > 1 file changed, 51 insertions(+), 35 deletions(-) > > diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c > index 33e904d838f4..2a0a19172847 100644 > --- a/fs/xfs/xfs_buf.c > +++ b/fs/xfs/xfs_buf.c > @@ -55,11 +55,27 @@ static inline bool xfs_buf_is_uncached(struct xfs_buf *bp) > return bp->b_rhash_key == XFS_BUF_DADDR_NULL; > } > > +static inline void > +xfs_buf_set_flags( > + struct xfs_buf *bp, > + unsigned int flags) > +{ > + WRITE_ONCE(bp->b_flags, bp->b_flags | flags); > +} > + > +static inline void > +xfs_buf_clear_flags( > + struct xfs_buf *bp, > + unsigned int flags) > +{ > + WRITE_ONCE(bp->b_flags, bp->b_flags & ~flags); > +} > + > void > xfs_buf_set_uptodate( > struct xfs_buf *bp) > { > - bp->b_flags |= XBF_DONE; > + xfs_buf_set_flags(bp, XBF_DONE); > } > > /* > @@ -76,14 +92,14 @@ xfs_buf_stale( > { > ASSERT(xfs_buf_islocked(bp)); > > - bp->b_flags |= XBF_STALE; > + xfs_buf_set_flags(bp, XBF_STALE); > > /* > * Clear the delwri status so that a delwri queue walker will not > * flush this buffer to disk now that it is stale. The delwri queue has > * a reference to the buffer, so this is safe to do. > */ > - bp->b_flags &= ~_XBF_DELWRI_Q; > + xfs_buf_clear_flags(bp, _XBF_DELWRI_Q); > > spin_lock(&bp->b_lockref.lock); > atomic_set(&bp->b_lru_ref, 0); > @@ -97,8 +113,7 @@ xfs_buf_clear_stale( > struct xfs_buf *bp) > { > ASSERT(bp->b_flags & XBF_STALE); > - > - bp->b_flags &= ~XBF_STALE; > + xfs_buf_clear_flags(bp, XBF_STALE); > } > > static void > @@ -175,7 +190,7 @@ xfs_buf_alloc_kmem( > bp->b_addr = NULL; > return -ENOMEM; > } > - bp->b_flags |= _XBF_KMEM; > + xfs_buf_set_flags(bp, _XBF_KMEM); > trace_xfs_buf_backing_kmem(bp, _RET_IP_); > return 0; > } > @@ -307,7 +322,7 @@ xfs_buf_alloc( > INIT_LIST_HEAD(&bp->b_li_list); > bp->b_target = target; > bp->b_mount = target->bt_mount; > - bp->b_flags = flags; > + WRITE_ONCE(bp->b_flags, flags); > bp->b_rhash_key = map[0].bm_bn; > bp->b_length = 0; > bp->b_map_count = nmaps; > @@ -436,7 +451,7 @@ xfs_buf_find_lock( > return -ENOENT; > } > ASSERT((bp->b_flags & _XBF_DELWRI_Q) == 0); > - bp->b_flags &= _XBF_KMEM; > + xfs_buf_clear_flags(bp, ~_XBF_KMEM); Looks ok to me, though it took me a while to figure out that this line correctly preserves clearing every bit *except* _XBF_KMEM. --D > bp->b_ops = NULL; > } > return 0; > @@ -604,8 +619,9 @@ _xfs_buf_read( > { > ASSERT(bp->b_maps[0].bm_bn != XFS_BUF_DADDR_NULL); > > - bp->b_flags &= ~(XBF_WRITE | XBF_ASYNC | XBF_READ_AHEAD | XBF_DONE); > - bp->b_flags |= XBF_READ; > + xfs_buf_clear_flags(bp, XBF_WRITE | XBF_ASYNC | XBF_READ_AHEAD | > + XBF_DONE); > + xfs_buf_set_flags(bp, XBF_READ); > xfs_buf_submit(bp); > return xfs_buf_iowait(bp); > } > @@ -641,7 +657,7 @@ xfs_buf_reverify( > bp->b_ops = ops; > bp->b_ops->verify_read(bp); > if (bp->b_error) > - bp->b_flags &= ~XBF_DONE; > + xfs_buf_clear_flags(bp, XBF_DONE); > return bp->b_error; > } > > @@ -679,7 +695,7 @@ xfs_buf_read_map( > error = xfs_buf_reverify(bp, ops); > > /* We do not want read in the flags */ > - bp->b_flags &= ~XBF_READ; > + xfs_buf_clear_flags(bp, XBF_READ); > ASSERT(bp->b_ops != NULL || ops == NULL); > } > > @@ -704,7 +720,7 @@ xfs_buf_read_map( > if (!xlog_is_shutdown(target->bt_mount->m_log)) > xfs_buf_ioerror_alert(bp, fa); > > - bp->b_flags &= ~XBF_DONE; > + xfs_buf_clear_flags(bp, XBF_DONE); > xfs_buf_stale(bp); > xfs_buf_relse(bp); > > @@ -750,8 +766,8 @@ xfs_buf_readahead_map( > } > XFS_STATS_INC(target->bt_mount, xb_get_read); > bp->b_ops = ops; > - bp->b_flags &= ~(XBF_WRITE | XBF_DONE); > - bp->b_flags |= flags; > + xfs_buf_clear_flags(bp, XBF_WRITE | XBF_DONE); > + xfs_buf_set_flags(bp, flags); > percpu_counter_inc(&target->bt_readahead_count); > xfs_buf_submit(bp); > } > @@ -783,7 +799,7 @@ xfs_buf_read_uncached( > ASSERT(bp->b_map_count == 1); > bp->b_rhash_key = XFS_BUF_DADDR_NULL; > bp->b_maps[0].bm_bn = daddr; > - bp->b_flags |= XBF_READ; > + xfs_buf_set_flags(bp, XBF_READ); > bp->b_ops = ops; > > xfs_buf_submit(bp); > @@ -1077,14 +1093,14 @@ xfs_buf_ioend_handle_error( > > resubmit: > xfs_buf_ioerror(bp, 0); > - bp->b_flags |= (XBF_DONE | XBF_WRITE_FAIL); > + xfs_buf_set_flags(bp, XBF_DONE | XBF_WRITE_FAIL); > reinit_completion(&bp->b_iowait); > xfs_buf_submit(bp); > return true; > out_stale: > xfs_buf_stale(bp); > - bp->b_flags |= XBF_DONE; > - bp->b_flags &= ~XBF_WRITE; > + xfs_buf_set_flags(bp, XBF_DONE); > + xfs_buf_clear_flags(bp, XBF_WRITE); > trace_xfs_buf_error_relse(bp, _RET_IP_); > return false; > } > @@ -1109,7 +1125,7 @@ xfs_buf_ioend( > if (!bp->b_error && bp->b_ops) > bp->b_ops->verify_read(bp); > if (!bp->b_error) > - bp->b_flags |= XBF_DONE; > + xfs_buf_set_flags(bp, XBF_DONE); > if (bp->b_flags & XBF_READ_AHEAD) > percpu_counter_dec(&bp->b_target->bt_readahead_count); > } else { > @@ -1119,8 +1135,8 @@ xfs_buf_ioend( > return; > } > } else { > - bp->b_flags &= ~XBF_WRITE_FAIL; > - bp->b_flags |= XBF_DONE; > + xfs_buf_clear_flags(bp, XBF_WRITE_FAIL); > + xfs_buf_set_flags(bp, XBF_DONE); > } > > /* clear the retry state */ > @@ -1140,7 +1156,7 @@ xfs_buf_ioend( > bp->b_iodone(bp); > } > > - bp->b_flags &= ~(XBF_READ | XBF_WRITE | XBF_READ_AHEAD); > + xfs_buf_clear_flags(bp, XBF_READ | XBF_WRITE | XBF_READ_AHEAD); > if (async) > xfs_buf_relse(bp); > } > @@ -1186,8 +1202,8 @@ xfs_buf_fail( > { > ASSERT(xfs_buf_islocked(bp)); > > - bp->b_flags |= XBF_ASYNC; > - bp->b_flags &= ~XBF_DONE; > + xfs_buf_set_flags(bp, XBF_ASYNC); > + xfs_buf_clear_flags(bp, XBF_DONE); > xfs_buf_stale(bp); > xfs_buf_ioerror(bp, -EIO); > xfs_buf_ioend(bp); > @@ -1201,9 +1217,9 @@ xfs_bwrite( > > ASSERT(xfs_buf_islocked(bp)); > > - bp->b_flags |= XBF_WRITE; > - bp->b_flags &= ~(XBF_ASYNC | XBF_READ | _XBF_DELWRI_Q | > - XBF_DONE); > + xfs_buf_set_flags(bp, XBF_WRITE); > + xfs_buf_clear_flags(bp, XBF_ASYNC | XBF_READ | _XBF_DELWRI_Q | > + XBF_DONE); > > xfs_buf_submit(bp); > error = xfs_buf_iowait(bp); > @@ -1394,7 +1410,7 @@ xfs_buf_submit( > return; > > ioerror: > - bp->b_flags &= ~XBF_DONE; > + xfs_buf_clear_flags(bp, XBF_DONE); > xfs_buf_stale(bp); > end_io: > if (bp->b_flags & XBF_ASYNC) > @@ -1805,7 +1821,7 @@ xfs_buf_delwri_cancel( > bp = list_first_entry(list, struct xfs_buf, b_list); > > xfs_buf_lock(bp); > - bp->b_flags &= ~_XBF_DELWRI_Q; > + xfs_buf_clear_flags(bp, _XBF_DELWRI_Q); > xfs_buf_list_del(bp); > xfs_buf_relse(bp); > } > @@ -1850,7 +1866,7 @@ xfs_buf_delwri_queue( > * might get readded to a delwri list after the synchronous writeout, in > * which case we need just need to re-add the flag here. > */ > - bp->b_flags |= _XBF_DELWRI_Q; > + xfs_buf_set_flags(bp, _XBF_DELWRI_Q); > if (list_empty(&bp->b_list)) { > xfs_buf_hold(bp); > list_add_tail(&bp->b_list, list); > @@ -1927,8 +1943,8 @@ xfs_buf_delwri_submit_prep( > } > > trace_xfs_buf_delwri_split(bp, _RET_IP_); > - bp->b_flags &= ~_XBF_DELWRI_Q; > - bp->b_flags |= XBF_WRITE; > + xfs_buf_clear_flags(bp, _XBF_DELWRI_Q); > + xfs_buf_set_flags(bp, XBF_WRITE); > return true; > } > > @@ -1969,7 +1985,7 @@ xfs_buf_delwri_submit_nowait( > } > if (!xfs_buf_delwri_submit_prep(bp)) > continue; > - bp->b_flags |= XBF_ASYNC; > + xfs_buf_set_flags(bp, XBF_ASYNC); > xfs_buf_list_del(bp); > xfs_buf_submit(bp); > } > @@ -2002,7 +2018,7 @@ xfs_buf_delwri_submit( > xfs_buf_lock(bp); > if (!xfs_buf_delwri_submit_prep(bp)) > continue; > - bp->b_flags &= ~XBF_ASYNC; > + xfs_buf_clear_flags(bp, XBF_ASYNC); > list_move_tail(&bp->b_list, &wait_list); > xfs_buf_submit(bp); > } > -- > 2.53.0 > >