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Date: Wed, 19 Feb 2020 11:44:22 +0100
From: Jan Kara <jack@...e.cz>
To: Eric Biggers <ebiggers@...nel.org>
Cc: linux-ext4@...r.kernel.org, Theodore Ts'o <tytso@....edu>,
Jan Kara <jack@...e.cz>
Subject: Re: [PATCH v2] ext4: fix race between writepages and enabling
EXT4_EXTENTS_FL
On Tue 18-02-20 21:35:23, Eric Biggers wrote:
> From: Eric Biggers <ebiggers@...gle.com>
>
> 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_journal_flag_rwsem -- renamed to s_writepages_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@...kaller.appspotmail.com
> Fixes: 6b523df4fb5a ("ext4: use transaction reservation for extent conversion in ext4_end_io")
> Cc: stable@...nel.org
> Signed-off-by: Eric Biggers <ebiggers@...gle.com>
The patch looks good to me. Just I'd split out the renaming to a separate
patch.
Honza
> ---
>
> v2: Instead of making ext4_writepages() read EXT4_EXTENTS_FL only once,
> make it so that EXT4_EXTENTS_FL can't be changed while
> ext4_writepages() is running.
>
> fs/ext4/ext4.h | 7 +++++--
> fs/ext4/inode.c | 14 +++++++-------
> fs/ext4/migrate.c | 27 +++++++++++++++++++--------
> fs/ext4/super.c | 6 +++---
> 4 files changed, 34 insertions(+), 20 deletions(-)
>
> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
> index 4441331d06cc4..0a59006c621a0 100644
> --- a/fs/ext4/ext4.h
> +++ b/fs/ext4/ext4.h
> @@ -1552,8 +1552,11 @@ 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. */
> - struct percpu_rw_semaphore s_journal_flag_rwsem;
> + /*
> + * 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
> unsigned long s_simulate_fail;
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index e60aca791d3f1..3b782eecf6563 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -2628,7 +2628,7 @@ static int ext4_writepages(struct address_space *mapping,
> if (unlikely(ext4_forced_shutdown(EXT4_SB(inode->i_sb))))
> return -EIO;
>
> - percpu_down_read(&sbi->s_journal_flag_rwsem);
> + percpu_down_read(&sbi->s_writepages_rwsem);
> trace_ext4_writepages(inode, wbc);
>
> /*
> @@ -2849,7 +2849,7 @@ static int ext4_writepages(struct address_space *mapping,
> out_writepages:
> trace_ext4_writepages_result(inode, wbc, ret,
> nr_to_write - wbc->nr_to_write);
> - percpu_up_read(&sbi->s_journal_flag_rwsem);
> + percpu_up_read(&sbi->s_writepages_rwsem);
> return ret;
> }
>
> @@ -2864,13 +2864,13 @@ static int ext4_dax_writepages(struct address_space *mapping,
> if (unlikely(ext4_forced_shutdown(EXT4_SB(inode->i_sb))))
> return -EIO;
>
> - percpu_down_read(&sbi->s_journal_flag_rwsem);
> + percpu_down_read(&sbi->s_writepages_rwsem);
> trace_ext4_writepages(inode, wbc);
>
> ret = dax_writeback_mapping_range(mapping, sbi->s_daxdev, wbc);
> trace_ext4_writepages_result(inode, wbc, ret,
> nr_to_write - wbc->nr_to_write);
> - percpu_up_read(&sbi->s_journal_flag_rwsem);
> + percpu_up_read(&sbi->s_writepages_rwsem);
> return ret;
> }
>
> @@ -5861,7 +5861,7 @@ int ext4_change_inode_journal_flag(struct inode *inode, int val)
> }
> }
>
> - percpu_down_write(&sbi->s_journal_flag_rwsem);
> + percpu_down_write(&sbi->s_writepages_rwsem);
> jbd2_journal_lock_updates(journal);
>
> /*
> @@ -5878,7 +5878,7 @@ int ext4_change_inode_journal_flag(struct inode *inode, int val)
> err = jbd2_journal_flush(journal);
> if (err < 0) {
> jbd2_journal_unlock_updates(journal);
> - percpu_up_write(&sbi->s_journal_flag_rwsem);
> + percpu_up_write(&sbi->s_writepages_rwsem);
> return err;
> }
> ext4_clear_inode_flag(inode, EXT4_INODE_JOURNAL_DATA);
> @@ -5886,7 +5886,7 @@ int ext4_change_inode_journal_flag(struct inode *inode, int val)
> ext4_set_aops(inode);
>
> jbd2_journal_unlock_updates(journal);
> - percpu_up_write(&sbi->s_journal_flag_rwsem);
> + percpu_up_write(&sbi->s_writepages_rwsem);
>
> if (val)
> up_write(&EXT4_I(inode)->i_mmap_sem);
> 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;
> }
> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index f464dff097748..f504c30170233 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -1054,7 +1054,7 @@ static void ext4_put_super(struct super_block *sb)
> percpu_counter_destroy(&sbi->s_freeinodes_counter);
> percpu_counter_destroy(&sbi->s_dirs_counter);
> percpu_counter_destroy(&sbi->s_dirtyclusters_counter);
> - percpu_free_rwsem(&sbi->s_journal_flag_rwsem);
> + percpu_free_rwsem(&sbi->s_writepages_rwsem);
> #ifdef CONFIG_QUOTA
> for (i = 0; i < EXT4_MAXQUOTAS; i++)
> kfree(get_qf_name(sb, sbi, i));
> @@ -4594,7 +4594,7 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
> err = percpu_counter_init(&sbi->s_dirtyclusters_counter, 0,
> GFP_KERNEL);
> if (!err)
> - err = percpu_init_rwsem(&sbi->s_journal_flag_rwsem);
> + err = percpu_init_rwsem(&sbi->s_writepages_rwsem);
>
> if (err) {
> ext4_msg(sb, KERN_ERR, "insufficient memory");
> @@ -4688,7 +4688,7 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
> percpu_counter_destroy(&sbi->s_freeinodes_counter);
> percpu_counter_destroy(&sbi->s_dirs_counter);
> percpu_counter_destroy(&sbi->s_dirtyclusters_counter);
> - percpu_free_rwsem(&sbi->s_journal_flag_rwsem);
> + percpu_free_rwsem(&sbi->s_writepages_rwsem);
> failed_mount5:
> ext4_ext_release(sb);
> ext4_release_system_zone(sb);
> --
> 2.25.0
>
--
Jan Kara <jack@...e.com>
SUSE Labs, CR
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