diff options
author | Eric Biggers <ebiggers@google.com> | 2020-02-19 19:30:47 +0100 |
---|---|---|
committer | Theodore Ts'o <tytso@mit.edu> | 2020-02-22 01:32:07 +0100 |
commit | cb85f4d23f794e24127f3e562cb3b54b0803f456 (patch) | |
tree | 8a8bf16b434a1f9e78b91220ef8eca39cc31a47f /fs | |
parent | ext4: rename s_journal_flag_rwsem to s_writepages_rwsem (diff) | |
download | linux-cb85f4d23f794e24127f3e562cb3b54b0803f456.tar.xz linux-cb85f4d23f794e24127f3e562cb3b54b0803f456.zip |
ext4: fix race between writepages and enabling EXT4_EXTENTS_FL
If EXT4_EXTENTS_FL is set on an inode while ext4_writepages() is running
on it, the following warning in ext4_add_complete_io() can be hit:
WARNING: CPU: 1 PID: 0 at fs/ext4/page-io.c:234 ext4_put_io_end_defer+0xf0/0x120
Here's a minimal reproducer (not 100% reliable) (root isn't required):
while true; do
sync
done &
while true; do
rm -f file
touch file
chattr -e file
echo X >> file
chattr +e file
done
The problem is that in ext4_writepages(), ext4_should_dioread_nolock()
(which only returns true on extent-based files) is checked once to set
the number of reserved journal credits, and also again later to select
the flags for ext4_map_blocks() and copy the reserved journal handle to
ext4_io_end::handle. But if EXT4_EXTENTS_FL is being concurrently set,
the first check can see dioread_nolock disabled while the later one can
see it enabled, causing the reserved handle to unexpectedly be NULL.
Since changing EXT4_EXTENTS_FL is uncommon, and there may be other races
related to doing so as well, fix this by synchronizing changing
EXT4_EXTENTS_FL with ext4_writepages() via the existing
s_writepages_rwsem (previously called s_journal_flag_rwsem).
This was originally reported by syzbot without a reproducer at
https://syzkaller.appspot.com/bug?extid=2202a584a00fffd19fbf,
but now that dioread_nolock is the default I also started seeing this
when running syzkaller locally.
Link: https://lore.kernel.org/r/20200219183047.47417-3-ebiggers@kernel.org
Reported-by: syzbot+2202a584a00fffd19fbf@syzkaller.appspotmail.com
Fixes: 6b523df4fb5a ("ext4: use transaction reservation for extent conversion in ext4_end_io")
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: Jan Kara <jack@suse.cz>
Cc: stable@kernel.org
Diffstat (limited to 'fs')
-rw-r--r-- | fs/ext4/ext4.h | 5 | ||||
-rw-r--r-- | fs/ext4/migrate.c | 27 |
2 files changed, 23 insertions, 9 deletions
diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h index 4b986ad42b9d..61b37a052052 100644 --- a/fs/ext4/ext4.h +++ b/fs/ext4/ext4.h @@ -1552,7 +1552,10 @@ struct ext4_sb_info { struct ratelimit_state s_warning_ratelimit_state; struct ratelimit_state s_msg_ratelimit_state; - /* Barrier between changing inodes' journal flags and writepages ops. */ + /* + * Barrier between writepages ops and changing any inode's JOURNAL_DATA + * or EXTENTS flag. + */ struct percpu_rw_semaphore s_writepages_rwsem; struct dax_device *s_daxdev; #ifdef CONFIG_EXT4_DEBUG diff --git a/fs/ext4/migrate.c b/fs/ext4/migrate.c index 89725fa42573..fb6520f37135 100644 --- a/fs/ext4/migrate.c +++ b/fs/ext4/migrate.c @@ -407,6 +407,7 @@ static int free_ext_block(handle_t *handle, struct inode *inode) int ext4_ext_migrate(struct inode *inode) { + struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb); handle_t *handle; int retval = 0, i; __le32 *i_data; @@ -431,6 +432,8 @@ int ext4_ext_migrate(struct inode *inode) */ return retval; + percpu_down_write(&sbi->s_writepages_rwsem); + /* * Worst case we can touch the allocation bitmaps, a bgd * block, and a block to link in the orphan list. We do need @@ -441,7 +444,7 @@ int ext4_ext_migrate(struct inode *inode) if (IS_ERR(handle)) { retval = PTR_ERR(handle); - return retval; + goto out_unlock; } goal = (((inode->i_ino - 1) / EXT4_INODES_PER_GROUP(inode->i_sb)) * EXT4_INODES_PER_GROUP(inode->i_sb)) + 1; @@ -452,7 +455,7 @@ int ext4_ext_migrate(struct inode *inode) if (IS_ERR(tmp_inode)) { retval = PTR_ERR(tmp_inode); ext4_journal_stop(handle); - return retval; + goto out_unlock; } i_size_write(tmp_inode, i_size_read(inode)); /* @@ -494,7 +497,7 @@ int ext4_ext_migrate(struct inode *inode) */ ext4_orphan_del(NULL, tmp_inode); retval = PTR_ERR(handle); - goto out; + goto out_tmp_inode; } ei = EXT4_I(inode); @@ -576,10 +579,11 @@ err_out: ext4_ext_tree_init(handle, tmp_inode); out_stop: ext4_journal_stop(handle); -out: +out_tmp_inode: unlock_new_inode(tmp_inode); iput(tmp_inode); - +out_unlock: + percpu_up_write(&sbi->s_writepages_rwsem); return retval; } @@ -589,7 +593,8 @@ out: int ext4_ind_migrate(struct inode *inode) { struct ext4_extent_header *eh; - struct ext4_super_block *es = EXT4_SB(inode->i_sb)->s_es; + struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb); + struct ext4_super_block *es = sbi->s_es; struct ext4_inode_info *ei = EXT4_I(inode); struct ext4_extent *ex; unsigned int i, len; @@ -613,9 +618,13 @@ int ext4_ind_migrate(struct inode *inode) if (test_opt(inode->i_sb, DELALLOC)) ext4_alloc_da_blocks(inode); + percpu_down_write(&sbi->s_writepages_rwsem); + handle = ext4_journal_start(inode, EXT4_HT_MIGRATE, 1); - if (IS_ERR(handle)) - return PTR_ERR(handle); + if (IS_ERR(handle)) { + ret = PTR_ERR(handle); + goto out_unlock; + } down_write(&EXT4_I(inode)->i_data_sem); ret = ext4_ext_check_inode(inode); @@ -650,5 +659,7 @@ int ext4_ind_migrate(struct inode *inode) errout: ext4_journal_stop(handle); up_write(&EXT4_I(inode)->i_data_sem); +out_unlock: + percpu_up_write(&sbi->s_writepages_rwsem); return ret; } |