From: Jan Kara <jack@xxxxxxx>
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@xxxxxxxxxxxxxxxxxxxxxxxxx
Link: https://lore.kernel.org/all/0000000000004c66b405fa108e27@xxxxxxxxxx
Fixes: c8585c6fcaf2 ("ext4: fix races between changing inode journal mode and ext4_writepages")
CC: stable@xxxxxxxxxxxxxxx
Signed-off-by: Jan Kara <jack@xxxxxxx>
Link: https://lore.kernel.org/r/20230504124723.20205-1-jack@xxxxxxx
Signed-off-by: Theodore Ts'o <tytso@xxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
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;
}
