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ext4: Move to shared i_rwsem even without dioread_nolock mount opt

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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>
This commit is contained in:
Ritesh Harjani 2019-12-12 11:25:57 +05:30 committed by Theodore Ts'o
parent aa9714d0e3
commit bc6385dab1
1 changed files with 3 additions and 6 deletions
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9
fs/ext4/file.c
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@ -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;