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ext4: fix locking for O_APPEND writes

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Al Viro pointed out that locking for O_APPEND writes was problematic,
since the location of the write isn't known until after we take the
i_mutex, which impacts the ext4_unaligned_aio() and s_bitmap_maxbytes
check.

For O_APPEND always assume that the write is unaligned so call
ext4_unwritten_wait().  And to solve the second problem, take the
i_mutex earlier before we start the s_bitmap_maxbytes check.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
This commit is contained in:
Theodore Ts'o
2014-04-21 14:37:52 -04:00
parent 7ed07ba8c3
commit f5ccfe1ddb
1 changed files with 26 additions and 16 deletions
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fs/ext4/file.c
+26 -16
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@@ -106,17 +106,37 @@ ext4_file_write(struct kiocb *iocb, const struct iovec *iov,
BUG_ON(iocb->ki_pos != pos); BUG_ON(iocb->ki_pos != pos);
/*
* Unaligned direct AIO must be serialized; see comment above
* In the case of O_APPEND, assume that we must always serialize
*/
if (o_direct &&
ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS) &&
!is_sync_kiocb(iocb) &&
(file->f_flags & O_APPEND ||
ext4_unaligned_aio(inode, iov, nr_segs, pos))) {
aio_mutex = ext4_aio_mutex(inode);
mutex_lock(aio_mutex);
ext4_unwritten_wait(inode);
}
mutex_lock(&inode->i_mutex);
if (file->f_flags & O_APPEND)
iocb->ki_pos = pos = i_size_read(inode);
/* /*
* If we have encountered a bitmap-format file, the size limit * If we have encountered a bitmap-format file, the size limit
* is smaller than s_maxbytes, which is for extent-mapped files. * is smaller than s_maxbytes, which is for extent-mapped files.
*/ */
if (!(ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS))) { if (!(ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS))) {
struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb); struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
if ((pos > sbi->s_bitmap_maxbytes || if ((pos > sbi->s_bitmap_maxbytes) ||
(pos == sbi->s_bitmap_maxbytes && length > 0))) (pos == sbi->s_bitmap_maxbytes && length > 0)) {
return -EFBIG; mutex_unlock(&inode->i_mutex);
ret = -EFBIG;
goto errout;
}
if (pos + length > sbi->s_bitmap_maxbytes) { if (pos + length > sbi->s_bitmap_maxbytes) {
nr_segs = iov_shorten((struct iovec *)iov, nr_segs, nr_segs = iov_shorten((struct iovec *)iov, nr_segs,
@@ -125,16 +145,6 @@ ext4_file_write(struct kiocb *iocb, const struct iovec *iov,
} }
if (o_direct) { if (o_direct) {
/* Unaligned direct AIO must be serialized; see comment above */
if (ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS) &&
!is_sync_kiocb(iocb) &&
ext4_unaligned_aio(inode, iov, nr_segs, pos)) {
aio_mutex = ext4_aio_mutex(inode);
mutex_lock(aio_mutex);
ext4_unwritten_wait(inode);
}
mutex_lock(&inode->i_mutex);
blk_start_plug(&plug); blk_start_plug(&plug);
iocb->private = &overwrite; iocb->private = &overwrite;
@@ -167,8 +177,7 @@ ext4_file_write(struct kiocb *iocb, const struct iovec *iov,
if (err == len && (map.m_flags & EXT4_MAP_MAPPED)) if (err == len && (map.m_flags & EXT4_MAP_MAPPED))
overwrite = 1; overwrite = 1;
} }
} else }
mutex_lock(&inode->i_mutex);
ret = __generic_file_aio_write(iocb, iov, nr_segs); ret = __generic_file_aio_write(iocb, iov, nr_segs);
mutex_unlock(&inode->i_mutex); mutex_unlock(&inode->i_mutex);
@@ -183,6 +192,7 @@ ext4_file_write(struct kiocb *iocb, const struct iovec *iov,
if (o_direct) if (o_direct)
blk_finish_plug(&plug); blk_finish_plug(&plug);
errout:
if (aio_mutex) if (aio_mutex)
mutex_unlock(aio_mutex); mutex_unlock(aio_mutex);
return ret; return ret;