On Wed 19-02-20 10:30:47, Eric Biggers wrote: > From: Eric Biggers <ebiggers@xxxxxxxxxx> > > 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. > > Reported-by: syzbot+2202a584a00fffd19fbf@xxxxxxxxxxxxxxxxxxxxxxxxx > Fixes: 6b523df4fb5a ("ext4: use transaction reservation for extent conversion in ext4_end_io") > Cc: stable@xxxxxxxxxx > Signed-off-by: Eric Biggers <ebiggers@xxxxxxxxxx> The patch looks good to me. You can add: Reviewed-by: Jan Kara <jack@xxxxxxx> Honza > --- > fs/ext4/ext4.h | 5 ++++- > 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 487a7b430b9dd..0a59006c621a0 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 89725fa425732..fb6520f371355 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 @@ int ext4_ext_migrate(struct inode *inode) > 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 @@ int ext4_ext_migrate(struct inode *inode) > 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; > } > -- > 2.25.0 > -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR
