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);