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authorRyusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>2012-07-30 14:42:07 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2012-07-30 17:25:19 -0700
commit572d8b3945a31bee7c40d21556803e4807fd9141 (patch)
tree8988dde859a68d88280047f5214427b49ebcf5de
parentfe0627e7b3d32a41c16fac6e0af091991545865e (diff)
nilfs2: fix deadlock issue between chcp and thaw ioctls
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.ryusuke@lab.ntt.co.jp> Cc: Fernando Luis Vazquez Cao <fernando@oss.ntt.co.jp> Tested-by: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--fs/nilfs2/ioctl.c4
-rw-r--r--fs/nilfs2/super.c3
-rw-r--r--fs/nilfs2/the_nilfs.c1
-rw-r--r--fs/nilfs2/the_nilfs.h2
4 files changed, 8 insertions, 2 deletions
diff --git a/fs/nilfs2/ioctl.c b/fs/nilfs2/ioctl.c
index 06658caa18b..0b6387c67e6 100644
--- a/fs/nilfs2/ioctl.c
+++ b/fs/nilfs2/ioctl.c
@@ -182,7 +182,7 @@ static int nilfs_ioctl_change_cpmode(struct inode *inode, struct file *filp,
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(struct inode *inode, struct file *filp,
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_file(filp);
return ret;
diff --git a/fs/nilfs2/super.c b/fs/nilfs2/super.c
index a76d6ea51ff..6522cac6057 100644
--- a/fs/nilfs2/super.c
+++ b/fs/nilfs2/super.c
@@ -945,6 +945,8 @@ static int nilfs_attach_snapshot(struct super_block *s, __u64 cno,
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);
@@ -969,6 +971,7 @@ static int nilfs_attach_snapshot(struct super_block *s, __u64 cno,
ret = nilfs_get_root_dentry(s, root, root_dentry);
nilfs_put_root(root);
out:
+ mutex_unlock(&nilfs->ns_snapshot_mount_mutex);
return ret;
}
diff --git a/fs/nilfs2/the_nilfs.c b/fs/nilfs2/the_nilfs.c
index 501b7f8b739..41e6a04a561 100644
--- a/fs/nilfs2/the_nilfs.c
+++ b/fs/nilfs2/the_nilfs.c
@@ -76,6 +76,7 @@ struct the_nilfs *alloc_nilfs(struct block_device *bdev)
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);
diff --git a/fs/nilfs2/the_nilfs.h b/fs/nilfs2/the_nilfs.h
index ef40a510e2f..2558f320b82 100644
--- 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
@@ -100,6 +101,7 @@ struct the_nilfs {
struct block_device *ns_bdev;
struct rw_semaphore ns_sem;
+ struct mutex ns_snapshot_mount_mutex;
/*
* used for