* [PATCH 6.11 43/63] netfs: Downgrade i_rwsem for a buffered write
[not found] <20241115063725.892410236@linuxfoundation.org>
@ 2024-11-15 6:38 ` Greg Kroah-Hartman
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From: Greg Kroah-Hartman @ 2024-11-15 6:38 UTC (permalink / raw)
To: stable
Cc: Greg Kroah-Hartman, patches, David Howells, Steve French,
Paulo Alcantara, Trond Myklebust, Jeff Layton, netfs, linux-cifs,
linux-nfs, linux-fsdevel, Christian Brauner, Sasha Levin
6.11-stable review patch. If anyone has any objections, please let me know.
------------------
From: David Howells <dhowells@redhat.com>
[ Upstream commit d6a77668a708f0b5ca6713b39c178c9d9563c35b ]
In the I/O locking code borrowed from NFS into netfslib, i_rwsem is held
locked across a buffered write - but this causes a performance regression
in cifs as it excludes buffered reads for the duration (cifs didn't use any
locking for buffered reads).
Mitigate this somewhat by downgrading the i_rwsem to a read lock across the
buffered write. This at least allows parallel reads to occur whilst
excluding other writes, DIO, truncate and setattr.
Note that this shouldn't be a problem for a buffered write as a read
through an mmap can circumvent i_rwsem anyway.
Also note that we might want to make this change in NFS also.
Signed-off-by: David Howells <dhowells@redhat.com>
Link: https://lore.kernel.org/r/1317958.1729096113@warthog.procyon.org.uk
cc: Steve French <sfrench@samba.org>
cc: Paulo Alcantara <pc@manguebit.com>
cc: Trond Myklebust <trondmy@kernel.org>
cc: Jeff Layton <jlayton@kernel.org>
cc: netfs@lists.linux.dev
cc: linux-cifs@vger.kernel.org
cc: linux-nfs@vger.kernel.org
cc: linux-fsdevel@vger.kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
fs/netfs/locking.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/fs/netfs/locking.c b/fs/netfs/locking.c
index 75dc52a49b3a4..709a6aa101028 100644
--- a/fs/netfs/locking.c
+++ b/fs/netfs/locking.c
@@ -121,6 +121,7 @@ int netfs_start_io_write(struct inode *inode)
up_write(&inode->i_rwsem);
return -ERESTARTSYS;
}
+ downgrade_write(&inode->i_rwsem);
return 0;
}
EXPORT_SYMBOL(netfs_start_io_write);
@@ -135,7 +136,7 @@ EXPORT_SYMBOL(netfs_start_io_write);
void netfs_end_io_write(struct inode *inode)
__releases(inode->i_rwsem)
{
- up_write(&inode->i_rwsem);
+ up_read(&inode->i_rwsem);
}
EXPORT_SYMBOL(netfs_end_io_write);
--
2.43.0
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