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ext4: fix crashes in dioread_nolock mode

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Competing overwrite DIO in dioread_nolock mode will just overwrite
pointer to io_end in the inode. This may result in data corruption or
extent conversion happening from IO completion interrupt because we
don't properly set buffer_defer_completion() when unlocked DIO races
with locked DIO to unwritten extent.

Since unlocked DIO doesn't need io_end for anything, just avoid
allocating it and corrupting pointer from inode for locked DIO.
A cleaner fix would be to avoid these games with io_end pointer from the
inode but that requires more intrusive changes so we leave that for
later.

Cc: stable@vger.kernel.org
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
This commit is contained in:
Jan Kara 2016-02-19 00:33:21 -05:00 committed by Theodore Ts'o
parent ed8ad83808
commit 74dae42785
1 changed files with 20 additions and 20 deletions
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40
fs/ext4/inode.c
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@ -3281,29 +3281,29 @@ static ssize_t ext4_ext_direct_IO(struct kiocb *iocb, struct iov_iter *iter,
* case, we allocate an io_end structure to hook to the iocb.
*/
iocb->private = NULL;
ext4_inode_aio_set(inode, NULL);
if (!is_sync_kiocb(iocb)) {
io_end = ext4_init_io_end(inode, GFP_NOFS);
if (!io_end) {
ret = -ENOMEM;
goto retake_lock;
}
/*
* Grab reference for DIO. Will be dropped in ext4_end_io_dio()
*/
iocb->private = ext4_get_io_end(io_end);
/*
* we save the io structure for current async direct
* IO, so that later ext4_map_blocks() could flag the
* io structure whether there is a unwritten extents
* needs to be converted when IO is completed.
*/
ext4_inode_aio_set(inode, io_end);
}
if (overwrite) {
get_block_func = ext4_get_block_overwrite;
} else {
ext4_inode_aio_set(inode, NULL);
if (!is_sync_kiocb(iocb)) {
io_end = ext4_init_io_end(inode, GFP_NOFS);
if (!io_end) {
ret = -ENOMEM;
goto retake_lock;
}
/*
* Grab reference for DIO. Will be dropped in
* ext4_end_io_dio()
*/
iocb->private = ext4_get_io_end(io_end);
/*
* we save the io structure for current async direct
* IO, so that later ext4_map_blocks() could flag the
* io structure whether there is a unwritten extents
* needs to be converted when IO is completed.
*/
ext4_inode_aio_set(inode, io_end);
}
get_block_func = ext4_get_block_write;
dio_flags = DIO_LOCKING;
}