From: Jan Kara jack@suse.cz
commit 00d873c17e29cc32d90ca852b82685f1673acaa5 upstream.
Ext4 has a filesystem wide lock protecting ext4_writepages() calls to avoid races with switching of journalled data flag or inode format. This lock can however cause a deadlock like:
CPU0 CPU1
ext4_writepages() percpu_down_read(sbi->s_writepages_rwsem); ext4_change_inode_journal_flag() percpu_down_write(sbi->s_writepages_rwsem); - blocks, all readers block from now on ext4_do_writepages() ext4_init_io_end() kmem_cache_zalloc(io_end_cachep, GFP_KERNEL) fs_reclaim frees dentry... dentry_unlink_inode() iput() - last ref => iput_final() - inode dirty => write_inode_now()... ext4_writepages() tries to acquire sbi->s_writepages_rwsem and blocks forever
Make sure we cannot recurse into filesystem reclaim from writeback code to avoid the deadlock.
Reported-by: syzbot+6898da502aef574c5f8a@syzkaller.appspotmail.com Link: https://lore.kernel.org/all/0000000000004c66b405fa108e27@google.com Fixes: c8585c6fcaf2 ("ext4: fix races between changing inode journal mode and ext4_writepages") CC: stable@vger.kernel.org Signed-off-by: Jan Kara jack@suse.cz Link: https://lore.kernel.org/r/20230504124723.20205-1-jack@suse.cz Signed-off-by: Theodore Ts'o tytso@mit.edu Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- fs/ext4/ext4.h | 24 ++++++++++++++++++++++++ fs/ext4/inode.c | 18 ++++++++++-------- fs/ext4/migrate.c | 11 ++++++----- 3 files changed, 40 insertions(+), 13 deletions(-)
--- a/fs/ext4/ext4.h +++ b/fs/ext4/ext4.h @@ -1774,6 +1774,30 @@ static inline struct ext4_inode_info *EX return container_of(inode, struct ext4_inode_info, vfs_inode); }
+static inline int ext4_writepages_down_read(struct super_block *sb) +{ + percpu_down_read(&EXT4_SB(sb)->s_writepages_rwsem); + return memalloc_nofs_save(); +} + +static inline void ext4_writepages_up_read(struct super_block *sb, int ctx) +{ + memalloc_nofs_restore(ctx); + percpu_up_read(&EXT4_SB(sb)->s_writepages_rwsem); +} + +static inline int ext4_writepages_down_write(struct super_block *sb) +{ + percpu_down_write(&EXT4_SB(sb)->s_writepages_rwsem); + return memalloc_nofs_save(); +} + +static inline void ext4_writepages_up_write(struct super_block *sb, int ctx) +{ + memalloc_nofs_restore(ctx); + percpu_up_write(&EXT4_SB(sb)->s_writepages_rwsem); +} + static inline int ext4_valid_inum(struct super_block *sb, unsigned long ino) { return ino == EXT4_ROOT_INO || --- a/fs/ext4/inode.c +++ b/fs/ext4/inode.c @@ -2956,13 +2956,14 @@ static int ext4_writepages(struct addres .can_map = 1, }; int ret; + int alloc_ctx;
if (unlikely(ext4_forced_shutdown(EXT4_SB(sb)))) return -EIO;
- percpu_down_read(&EXT4_SB(sb)->s_writepages_rwsem); + alloc_ctx = ext4_writepages_down_read(sb); ret = ext4_do_writepages(&mpd); - percpu_up_read(&EXT4_SB(sb)->s_writepages_rwsem); + ext4_writepages_up_read(sb, alloc_ctx);
return ret; } @@ -2990,17 +2991,18 @@ static int ext4_dax_writepages(struct ad long nr_to_write = wbc->nr_to_write; struct inode *inode = mapping->host; struct ext4_sb_info *sbi = EXT4_SB(mapping->host->i_sb); + int alloc_ctx;
if (unlikely(ext4_forced_shutdown(EXT4_SB(inode->i_sb)))) return -EIO;
- percpu_down_read(&sbi->s_writepages_rwsem); + alloc_ctx = ext4_writepages_down_read(inode->i_sb); 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_writepages_rwsem); + ext4_writepages_up_read(inode->i_sb, alloc_ctx); return ret; }
@@ -6122,7 +6124,7 @@ int ext4_change_inode_journal_flag(struc journal_t *journal; handle_t *handle; int err; - struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb); + int alloc_ctx;
/* * We have to be very careful here: changing a data block's @@ -6160,7 +6162,7 @@ int ext4_change_inode_journal_flag(struc } }
- percpu_down_write(&sbi->s_writepages_rwsem); + alloc_ctx = ext4_writepages_down_write(inode->i_sb); jbd2_journal_lock_updates(journal);
/* @@ -6177,7 +6179,7 @@ int ext4_change_inode_journal_flag(struc err = jbd2_journal_flush(journal, 0); if (err < 0) { jbd2_journal_unlock_updates(journal); - percpu_up_write(&sbi->s_writepages_rwsem); + ext4_writepages_up_write(inode->i_sb, alloc_ctx); return err; } ext4_clear_inode_flag(inode, EXT4_INODE_JOURNAL_DATA); @@ -6185,7 +6187,7 @@ int ext4_change_inode_journal_flag(struc ext4_set_aops(inode);
jbd2_journal_unlock_updates(journal); - percpu_up_write(&sbi->s_writepages_rwsem); + ext4_writepages_up_write(inode->i_sb, alloc_ctx);
if (val) filemap_invalidate_unlock(inode->i_mapping); --- a/fs/ext4/migrate.c +++ b/fs/ext4/migrate.c @@ -408,7 +408,6 @@ static int free_ext_block(handle_t *hand
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; @@ -418,6 +417,7 @@ int ext4_ext_migrate(struct inode *inode unsigned long max_entries; __u32 goal, tmp_csum_seed; uid_t owner[2]; + int alloc_ctx;
/* * If the filesystem does not support extents, or the inode @@ -434,7 +434,7 @@ int ext4_ext_migrate(struct inode *inode */ return retval;
- percpu_down_write(&sbi->s_writepages_rwsem); + alloc_ctx = ext4_writepages_down_write(inode->i_sb);
/* * Worst case we can touch the allocation bitmaps and a block @@ -586,7 +586,7 @@ out_tmp_inode: unlock_new_inode(tmp_inode); iput(tmp_inode); out_unlock: - percpu_up_write(&sbi->s_writepages_rwsem); + ext4_writepages_up_write(inode->i_sb, alloc_ctx); return retval; }
@@ -605,6 +605,7 @@ int ext4_ind_migrate(struct inode *inode ext4_fsblk_t blk; handle_t *handle; int ret, ret2 = 0; + int alloc_ctx;
if (!ext4_has_feature_extents(inode->i_sb) || (!ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS))) @@ -621,7 +622,7 @@ 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); + alloc_ctx = ext4_writepages_down_write(inode->i_sb);
handle = ext4_journal_start(inode, EXT4_HT_MIGRATE, 1); if (IS_ERR(handle)) { @@ -665,6 +666,6 @@ errout: ext4_journal_stop(handle); up_write(&EXT4_I(inode)->i_data_sem); out_unlock: - percpu_up_write(&sbi->s_writepages_rwsem); + ext4_writepages_up_write(inode->i_sb, alloc_ctx); return ret; }