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ext4: Move to shared i_rwsem even without dioread_nolock mount opt
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>
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1 changed files with 3 additions and 6 deletions
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@ -392,8 +392,8 @@ static const struct iomap_dio_ops ext4_dio_write_ops = {
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* - For extending writes case we don't take the shared lock, since it requires
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* updating inode i_disksize and/or orphan handling with exclusive lock.
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*
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* - shared locking will only be true mostly with overwrites in dioread_nolock
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* mode. Otherwise we will switch to exclusive i_rwsem lock.
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* - shared locking will only be true mostly with overwrites. Otherwise we will
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* switch to exclusive i_rwsem lock.
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*/
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static ssize_t ext4_dio_write_checks(struct kiocb *iocb, struct iov_iter *from,
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bool *ilock_shared, bool *extend)
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@ -415,14 +415,11 @@ static ssize_t ext4_dio_write_checks(struct kiocb *iocb, struct iov_iter *from,
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*extend = true;
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/*
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* Determine whether the IO operation will overwrite allocated
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* and initialized blocks. If so, check to see whether it is
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* possible to take the dioread_nolock path.
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*
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* and initialized blocks.
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* We need exclusive i_rwsem for changing security info
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* in file_modified().
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*/
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if (*ilock_shared && (!IS_NOSEC(inode) || *extend ||
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!ext4_should_dioread_nolock(inode) ||
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!ext4_overwrite_io(inode, offset, count))) {
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inode_unlock_shared(inode);
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*ilock_shared = false;
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