Commit 428bb08a authored Dec 12, 2019 by Ritesh Harjani Committed by Greg Kroah-Hartman Feb 24, 2020

ext4: fix ext4_dax_read/write inode locking sequence for IOCB_NOWAIT



[ Upstream commit f629afe3369e9885fd6e9cc7a4f514b6a65cf9e9 ]

Apparently our current rwsem code doesn't like doing the trylock, then
lock for real scheme.  So change our dax read/write methods to just do the
trylock for the RWF_NOWAIT case.
This seems to fix AIM7 regression in some scalable filesystems upto ~25%
in some cases. Claimed in commit 942491c9 ("xfs: fix AIM7 regression")

Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Matthew Bobrowski <mbobrowski@mbobrowski.org>
Tested-by: Joseph Qi <joseph.qi@linux.alibaba.com>
Signed-off-by: Ritesh Harjani <riteshh@linux.ibm.com>
Link: https://lore.kernel.org/r/20191212055557.11151-2-riteshh@linux.ibm.com


Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Sasha Levin <sashal@kernel.org>

parent 44d748f2

fs/ext4/file.c

+6 −4

Original line number	Diff line number	Diff line
		@@ -40,9 +40,10 @@ static ssize_t ext4_dax_read_iter(struct kiocb iocb, struct iov_iter to)
		struct inode *inode = file_inode(iocb->ki_filp);
		ssize_t ret;

		if (!inode_trylock_shared(inode)) {
		if (iocb->ki_flags & IOCB_NOWAIT)
		if (iocb->ki_flags & IOCB_NOWAIT) {
		if (!inode_trylock_shared(inode))
		return -EAGAIN;
		} else {
		inode_lock_shared(inode);
		}
		/*
		@@ -190,9 +191,10 @@ ext4_dax_write_iter(struct kiocb iocb, struct iov_iter from)
		struct inode *inode = file_inode(iocb->ki_filp);
		ssize_t ret;

		if (!inode_trylock(inode)) {
		if (iocb->ki_flags & IOCB_NOWAIT)
		if (iocb->ki_flags & IOCB_NOWAIT) {
		if (!inode_trylock(inode))
		return -EAGAIN;
		} else {
		inode_lock(inode);
		}
		ret = ext4_write_checks(iocb, from);