ext4: Move to shared i_rwsem even without dioread_nolock mount opt (bc6385da) · Commits · 戴 / test

We were using shared locking only in case of dioread_nolock mount option in case of DIO overwrites. This mount condition is not needed anymore with current code, since:- 1. No race between buffered writes & DIO overwrites. Since buffIO writes takes exclusive lock & DIO overwrites will take shared locking. Also DIO path will make sure to flush and wait for any dirty page cache data. 2. No race between buffered reads & DIO overwrites, since there is no block allocation that is possible with DIO overwrites. So no stale data exposure should happen. Same is the case between DIO reads & DIO overwrites. 3. Also other paths like truncate is protected, since we wait there for any DIO in flight to be over. Reviewed-by:

Jan Kara <jack@suse.cz> Tested-by:

Joseph Qi <joseph.qi@linux.alibaba.com> Signed-off-by:

Ritesh Harjani <riteshh@linux.ibm.com> Link: https://lore.kernel.org/r/20191212055557.11151-4-riteshh@linux.ibm.com Signed-off-by:

Theodore Ts'o <tytso@mit.edu>

fs/ext4/file.c

+3 −6

Original line number	Diff line number	Diff line
		@@ -392,8 +392,8 @@ static const struct iomap_dio_ops ext4_dio_write_ops = {
		* - For extending writes case we don't take the shared lock, since it requires
		* updating inode i_disksize and/or orphan handling with exclusive lock.
		*
		* - shared locking will only be true mostly with overwrites in dioread_nolock
		* mode. Otherwise we will switch to exclusive i_rwsem lock.
		* - shared locking will only be true mostly with overwrites. Otherwise we will
		* switch to exclusive i_rwsem lock.
		*/
		static ssize_t ext4_dio_write_checks(struct kiocb iocb, struct iov_iter from,
		bool ilock_shared, bool extend)
		@@ -415,14 +415,11 @@ restart:
		*extend = true;
		/*
		* Determine whether the IO operation will overwrite allocated
		* and initialized blocks. If so, check to see whether it is
		* possible to take the dioread_nolock path.
		*
		* and initialized blocks.
		* We need exclusive i_rwsem for changing security info
		* in file_modified().
		*/
		if (ilock_shared && (!IS_NOSEC(inode) \|\| extend \|\|
		!ext4_should_dioread_nolock(inode) \|\|
		!ext4_overwrite_io(inode, offset, count))) {
		inode_unlock_shared(inode);
		*ilock_shared = false;

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