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 E900542BEB9 for ; Tue, 28 Jul 2026 15:42:03 +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=1785253325; cv=none; b=GLxbfcCjP8RvzXpT4H/xjQoHihgneZ6F+ddMc+5GEkluhjB/qFe6g/s0PLHWDFLo2aBcs87ZojD1Li6KxRNAbrinrXuZBnb75HCOK94WrEYj5am5Lgjk9bRpcyh+RM2nO8BBUKi/iKQuCUnCWd3NBGvk1P5doidL8oETB/s4l/w= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785253325; c=relaxed/simple; bh=irLSJw8xwbLw7pmMj9czeIA/IcBg3QODY+CmHI1PcyE=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=uS6JwsQziNObMmFiYTUgyFeIx/CjiT4u+Po1rp6IyHeHlyIRDi/7IclFM0TUYKxsN40xr5mo4sZuL/E/N69LIMySAx1qGYO/g4zjTpNvuO1D7qZooZgDkfjsxm+fyWR44mP9GdVrSZmZAqO7+esfHmPyKoyf2T075xjo6FjmBio= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=TG6+Z5u6; 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="TG6+Z5u6" Received: by smtp.kernel.org (Postfix) with UTF8SMTPSA id DFFE11F000E9; Tue, 28 Jul 2026 15:42:02 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1785253323; bh=bSTeHuaObl+ztfbym8sGP9CXmlIT6vqKkwKLXM7ytVs=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=TG6+Z5u6QbswBlv/MYAJn+a/j9LXLhbhgEpIsDSlWnvjQBgAgQvQi0z0KTpeqaXW9 gX1mEBv739wXFdCOtLL/1+FVEVx+M3EN6fIXzsjui+Ve9rrj60smje6uCNjGOMKptJ y8RlG2yfKHqIfcCtA0oiVqPA1LSD/uphLfExRWNmcUofeI8JVAZEOAlGMnbTOC59KA 56ImnfSbL1E7ncsthHk7J4eZsg25IdT3gZPDfmQDzgNI5rqskTDA7wIb6VR4H8dvzy pweIVx+WYjANNNPEW3FrVosjLQDxsspJLkSZslZdZknjDSrAiX4Fa5XRXTPpiL7L+B NGf6rNnr0dAZA== Date: Tue, 28 Jul 2026 08:42:02 -0700 From: "Darrick J. Wong" To: Christoph Hellwig Cc: Carlos Maiolino , Brian Foster , linux-xfs@vger.kernel.org Subject: Re: [PATCH 02/12] xfs: consolidate buffer locking in xfs_buf_get_map Message-ID: <20260728154202.GQ2901224@frogsfrogsfrogs> References: <20260728081152.1778841-1-hch@lst.de> <20260728081152.1778841-3-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: <20260728081152.1778841-3-hch@lst.de> On Tue, Jul 28, 2026 at 10:11:10AM +0200, Christoph Hellwig wrote: > Consolidate the code to lock the buffer based on the passed in flags > into xfs_buf_get_map instead of having two different sites for buffer > lookup vs insertation. This requires initializing b_lock to unlocked on > allocation and doing an atomic for locking it for newly allocated buffers, > but greatly simplifies the logic. > > Signed-off-by: Christoph Hellwig > Reviewed-by: Brian Foster > --- > fs/xfs/xfs_buf.c | 73 +++++++++++++++++++++------------------------- > fs/xfs/xfs_trace.h | 2 +- > 2 files changed, 35 insertions(+), 40 deletions(-) > > diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c > index 16b9f3e50551..d4ab69112d11 100644 > --- a/fs/xfs/xfs_buf.c > +++ b/fs/xfs/xfs_buf.c > @@ -261,6 +261,19 @@ xfs_buf_alloc_backing_mem( > return xfs_buf_alloc_folio(bp, size, gfp_mask); > } > > +/* > + * Allocate a new buffer. > + * > + * The creator of a new buffer holds a lockref to that buffer. This ensures > + * that the buffer is owned by the caller and racing RCU lookups right after > + * inserting into the hash table are safe against freeing. > + * > + * Racing threads trying to look up the buffer will have to wait for b_sema to > + * do anything non-trivial. > + * > + * Note that b_sema is not locked at creation time, but only when a caller > + * wants to access the buffer. Yay comments :) Reviewed-by: "Darrick J. Wong" --D > + */ > static int > xfs_buf_alloc( > struct xfs_buftarg *target, > @@ -282,15 +295,8 @@ xfs_buf_alloc( > * specifically set by later operations on the buffer. > */ > flags &= ~(XBF_TRYLOCK | XBF_ASYNC | XBF_READ_AHEAD); > - > - /* > - * A new buffer is held and locked by the owner. This ensures that the > - * buffer is owned by the caller and racing RCU lookups right after > - * inserting into the hash table are safe (and will have to wait for > - * the unlock to do anything non-trivial). > - */ > lockref_init(&bp->b_lockref); > - sema_init(&bp->b_sema, 0); /* held, no waiters */ > + sema_init(&bp->b_sema, 1); /* unlocked */ > atomic_set(&bp->b_lru_ref, 1); > init_completion(&bp->b_iowait); > INIT_LIST_HEAD(&bp->b_lru); > @@ -433,33 +439,25 @@ xfs_buf_find_lock( > return 0; > } > > -static inline int > +static inline struct xfs_buf * > xfs_buf_lookup( > struct xfs_buftarg *btp, > - struct xfs_buf_map *map, > - xfs_buf_flags_t flags, > - struct xfs_buf **bpp) > + struct xfs_buf_map *map) > { > struct xfs_buf *bp; > - int error; > > rcu_read_lock(); > bp = rhashtable_lookup(&btp->bt_hash, map, xfs_buf_hash_params); > if (!bp || !lockref_get_not_dead(&bp->b_lockref)) { > rcu_read_unlock(); > - return -ENOENT; > + XFS_STATS_INC(btp->bt_mount, xb_miss_locked); > + return NULL; > } > rcu_read_unlock(); > > - error = xfs_buf_find_lock(bp, flags); > - if (error) { > - xfs_buf_rele(bp); > - return error; > - } > - > - trace_xfs_buf_find(bp, flags, _RET_IP_); > - *bpp = bp; > - return 0; > + trace_xfs_buf_find(bp, _RET_IP_); > + XFS_STATS_INC(btp->bt_mount, xb_get_locked); > + return bp; > } > > /* > @@ -512,11 +510,7 @@ xfs_buf_find_insert( > goto retry; > } > rcu_read_unlock(); > - error = xfs_buf_find_lock(bp, flags); > - if (error) > - xfs_buf_rele(bp); > - else > - *bpp = bp; > + *bpp = bp; > goto out_free_buf; > } > rcu_read_unlock(); > @@ -558,21 +552,20 @@ xfs_buf_get_map( > if (error) > return error; > > - error = xfs_buf_lookup(btp, &cmap, flags, &bp); > - if (error && error != -ENOENT) > - return error; > - > /* cache hits always outnumber misses by at least 10:1 */ > + bp = xfs_buf_lookup(btp, &cmap); > if (unlikely(!bp)) { > - XFS_STATS_INC(btp->bt_mount, xb_miss_locked); > - > if (flags & XBF_INCORE) > return -ENOENT; > error = xfs_buf_find_insert(btp, &cmap, map, nmaps, flags, &bp); > if (error) > return error; > - } else { > - XFS_STATS_INC(btp->bt_mount, xb_get_locked); > + } > + > + error = xfs_buf_find_lock(bp, flags); > + if (error) { > + xfs_buf_rele(bp); > + return error; > } > > /* > @@ -797,9 +790,11 @@ xfs_buf_get_uncached( > DEFINE_SINGLE_BUF_MAP(map, XFS_BUF_DADDR_NULL, numblks); > > error = xfs_buf_alloc(target, &map, 1, 0, bpp); > - if (!error) > - trace_xfs_buf_get_uncached(*bpp, _RET_IP_); > - return error; > + if (error) > + return error; > + xfs_buf_lock(*bpp); > + trace_xfs_buf_get_uncached(*bpp, _RET_IP_); > + return 0; > } > > /* > diff --git a/fs/xfs/xfs_trace.h b/fs/xfs/xfs_trace.h > index aeb89ac53bf1..f333c938fbd9 100644 > --- a/fs/xfs/xfs_trace.h > +++ b/fs/xfs/xfs_trace.h > @@ -792,6 +792,7 @@ DEFINE_BUF_EVENT(xfs_buf_backing_folio); > DEFINE_BUF_EVENT(xfs_buf_backing_kmem); > DEFINE_BUF_EVENT(xfs_buf_backing_vmalloc); > DEFINE_BUF_EVENT(xfs_buf_backing_fallback); > +DEFINE_BUF_EVENT(xfs_buf_find); > > /* not really buffer traces, but the buf provides useful information */ > DEFINE_BUF_EVENT(xfs_btree_corrupt); > @@ -837,7 +838,6 @@ DECLARE_EVENT_CLASS(xfs_buf_flags_class, > DEFINE_EVENT(xfs_buf_flags_class, name, \ > TP_PROTO(struct xfs_buf *bp, unsigned flags, unsigned long caller_ip), \ > TP_ARGS(bp, flags, caller_ip)) > -DEFINE_BUF_FLAGS_EVENT(xfs_buf_find); > DEFINE_BUF_FLAGS_EVENT(xfs_buf_get); > DEFINE_BUF_FLAGS_EVENT(xfs_buf_read); > DEFINE_BUF_FLAGS_EVENT(xfs_buf_readahead); > -- > 2.53.0 > >