Btrfs: fix NULL pointer crash when running balance and scrub concurrently
While running balance, scrub, fsstress concurrently we hit the
following kernel crash:
[56561.448845] BTRFS info (device sde): relocating block group 11005853696 flags 132
[56561.524077] BUG: unable to handle kernel NULL pointer dereference at 0000000000000078
[56561.524237] IP: [<ffffffffa038956d>] scrub_chunk.isra.12+0xdd/0x130 [btrfs]
[56561.524297] PGD 9be28067 PUD 7f3dd067 PMD 0
[56561.524325] Oops: 0000 [#1] SMP
[....]
[56561.527237] Call Trace:
[56561.527309] [<ffffffffa038980e>] scrub_enumerate_chunks+0x24e/0x490 [btrfs]
[56561.527392] [<ffffffff810abe00>] ? abort_exclusive_wait+0x50/0xb0
[56561.527476] [<ffffffffa038add4>] btrfs_scrub_dev+0x1a4/0x530 [btrfs]
[56561.527561] [<ffffffffa0368107>] btrfs_ioctl+0x13f7/0x2a90 [btrfs]
[56561.527639] [<ffffffff811c82f0>] do_vfs_ioctl+0x2e0/0x4c0
[56561.527712] [<ffffffff8109c384>] ? vtime_account_user+0x54/0x60
[56561.527788] [<ffffffff810f768c>] ? __audit_syscall_entry+0x9c/0xf0
[56561.527870] [<ffffffff811c8551>] SyS_ioctl+0x81/0xa0
[56561.527941] [<ffffffff815707f7>] tracesys+0xdd/0xe2
[...]
[56561.528304] RIP [<ffffffffa038956d>] scrub_chunk.isra.12+0xdd/0x130 [btrfs]
[56561.528395] RSP <ffff88004c0f5be8>
[56561.528454] CR2: 0000000000000078
This is because in btrfs_relocate_chunk(), we will free @bdev directly while
scrub may still hold extent mapping, and may access freed memory.
Fix this problem by wrapping freeing @bdev work into free_extent_map() which
is based on reference count.
Reported-by: Qu Wenruo <quwenruo@cn.fujitsu.com>
Signed-off-by: Wang Shilong <wangsl.fnst@cn.fujitsu.com>
Signed-off-by: Miao Xie <miaox@cn.fujitsu.com>
Signed-off-by: Chris Mason <clm@fb.com>
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index ffeed6d..19c298a 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -2543,9 +2543,6 @@
remove_extent_mapping(em_tree, em);
write_unlock(&em_tree->lock);
- kfree(map);
- em->bdev = NULL;
-
/* once for the tree */
free_extent_map(em);
/* once for us */
@@ -4301,9 +4298,11 @@
em = alloc_extent_map();
if (!em) {
+ kfree(map);
ret = -ENOMEM;
goto error;
}
+ set_bit(EXTENT_FLAG_FS_MAPPING, &em->flags);
em->bdev = (struct block_device *)map;
em->start = start;
em->len = num_bytes;
@@ -4346,7 +4345,6 @@
/* One for the tree reference */
free_extent_map(em);
error:
- kfree(map);
kfree(devices_info);
return ret;
}
@@ -4558,7 +4556,6 @@
write_unlock(&tree->map_tree.lock);
if (!em)
break;
- kfree(em->bdev);
/* once for us */
free_extent_map(em);
/* once for the tree */
@@ -5822,6 +5819,7 @@
return -ENOMEM;
}
+ set_bit(EXTENT_FLAG_FS_MAPPING, &em->flags);
em->bdev = (struct block_device *)map;
em->start = logical;
em->len = length;
@@ -5846,7 +5844,6 @@
map->stripes[i].dev = btrfs_find_device(root->fs_info, devid,
uuid, NULL);
if (!map->stripes[i].dev && !btrfs_test_opt(root, DEGRADED)) {
- kfree(map);
free_extent_map(em);
return -EIO;
}
@@ -5854,7 +5851,6 @@
map->stripes[i].dev =
add_missing_dev(root, devid, uuid);
if (!map->stripes[i].dev) {
- kfree(map);
free_extent_map(em);
return -EIO;
}