3.2-stable review patch. If anyone has any objections, please let me know.
------------------ From: Ryusuke Konishi <konishi.ryus...@lab.ntt.co.jp> commit 572d8b3945a31bee7c40d21556803e4807fd9141 upstream. An fs-thaw ioctl causes deadlock with a chcp or mkcp -s command: chcp D ffff88013870f3d0 0 1325 1324 0x00000004 ... Call Trace: nilfs_transaction_begin+0x11c/0x1a0 [nilfs2] wake_up_bit+0x20/0x20 copy_from_user+0x18/0x30 [nilfs2] nilfs_ioctl_change_cpmode+0x7d/0xcf [nilfs2] nilfs_ioctl+0x252/0x61a [nilfs2] do_page_fault+0x311/0x34c get_unmapped_area+0x132/0x14e do_vfs_ioctl+0x44b/0x490 __set_task_blocked+0x5a/0x61 vm_mmap_pgoff+0x76/0x87 __set_current_blocked+0x30/0x4a sys_ioctl+0x4b/0x6f system_call_fastpath+0x16/0x1b thaw D ffff88013870d890 0 1352 1351 0x00000004 ... Call Trace: rwsem_down_failed_common+0xdb/0x10f call_rwsem_down_write_failed+0x13/0x20 down_write+0x25/0x27 thaw_super+0x13/0x9e do_vfs_ioctl+0x1f5/0x490 vm_mmap_pgoff+0x76/0x87 sys_ioctl+0x4b/0x6f filp_close+0x64/0x6c system_call_fastpath+0x16/0x1b where the thaw ioctl deadlocked at thaw_super() when called while chcp was waiting at nilfs_transaction_begin() called from nilfs_ioctl_change_cpmode(). This deadlock is 100% reproducible. This is because nilfs_ioctl_change_cpmode() first locks sb->s_umount in read mode and then waits for unfreezing in nilfs_transaction_begin(), whereas thaw_super() locks sb->s_umount in write mode. The locking of sb->s_umount here was intended to make snapshot mounts and the downgrade of snapshots to checkpoints exclusive. This fixes the deadlock issue by replacing the sb->s_umount usage in nilfs_ioctl_change_cpmode() with a dedicated mutex which protects snapshot mounts. Signed-off-by: Ryusuke Konishi <konishi.ryus...@lab.ntt.co.jp> Cc: Fernando Luis Vazquez Cao <ferna...@oss.ntt.co.jp> Tested-by: Ryusuke Konishi <konishi.ryus...@lab.ntt.co.jp> Signed-off-by: Andrew Morton <a...@linux-foundation.org> Signed-off-by: Linus Torvalds <torva...@linux-foundation.org> Signed-off-by: Ben Hutchings <b...@decadent.org.uk> --- fs/nilfs2/ioctl.c | 4 ++-- fs/nilfs2/super.c | 3 +++ fs/nilfs2/the_nilfs.c | 1 + fs/nilfs2/the_nilfs.h | 2 ++ 4 files changed, 8 insertions(+), 2 deletions(-) --- a/fs/nilfs2/ioctl.c +++ b/fs/nilfs2/ioctl.c @@ -182,7 +182,7 @@ static int nilfs_ioctl_change_cpmode(str if (copy_from_user(&cpmode, argp, sizeof(cpmode))) goto out; - down_read(&inode->i_sb->s_umount); + mutex_lock(&nilfs->ns_snapshot_mount_mutex); nilfs_transaction_begin(inode->i_sb, &ti, 0); ret = nilfs_cpfile_change_cpmode( @@ -192,7 +192,7 @@ static int nilfs_ioctl_change_cpmode(str else nilfs_transaction_commit(inode->i_sb); /* never fails */ - up_read(&inode->i_sb->s_umount); + mutex_unlock(&nilfs->ns_snapshot_mount_mutex); out: mnt_drop_write(filp->f_path.mnt); return ret; --- a/fs/nilfs2/super.c +++ b/fs/nilfs2/super.c @@ -951,6 +951,8 @@ static int nilfs_attach_snapshot(struct struct nilfs_root *root; int ret; + mutex_lock(&nilfs->ns_snapshot_mount_mutex); + down_read(&nilfs->ns_segctor_sem); ret = nilfs_cpfile_is_snapshot(nilfs->ns_cpfile, cno); up_read(&nilfs->ns_segctor_sem); @@ -975,6 +977,7 @@ static int nilfs_attach_snapshot(struct ret = nilfs_get_root_dentry(s, root, root_dentry); nilfs_put_root(root); out: + mutex_unlock(&nilfs->ns_snapshot_mount_mutex); return ret; } --- a/fs/nilfs2/the_nilfs.c +++ b/fs/nilfs2/the_nilfs.c @@ -76,6 +76,7 @@ struct the_nilfs *alloc_nilfs(struct blo nilfs->ns_bdev = bdev; atomic_set(&nilfs->ns_ndirtyblks, 0); init_rwsem(&nilfs->ns_sem); + mutex_init(&nilfs->ns_snapshot_mount_mutex); INIT_LIST_HEAD(&nilfs->ns_dirty_files); INIT_LIST_HEAD(&nilfs->ns_gc_inodes); spin_lock_init(&nilfs->ns_inode_lock); --- a/fs/nilfs2/the_nilfs.h +++ b/fs/nilfs2/the_nilfs.h @@ -47,6 +47,7 @@ enum { * @ns_flags: flags * @ns_bdev: block device * @ns_sem: semaphore for shared states + * @ns_snapshot_mount_mutex: mutex to protect snapshot mounts * @ns_sbh: buffer heads of on-disk super blocks * @ns_sbp: pointers to super block data * @ns_sbwtime: previous write time of super block @@ -99,6 +100,7 @@ struct the_nilfs { struct block_device *ns_bdev; struct rw_semaphore ns_sem; + struct mutex ns_snapshot_mount_mutex; /* * used for -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/