From 50460e37186a2b932eacea24dca804bd1bcd2012 Mon Sep 17 00:00:00 2001 From: Filipe Manana Date: Fri, 20 Nov 2015 10:42:47 +0000 Subject: [PATCH] Btrfs: fix race when finishing dev replace leading to transaction abort During the final phase of a device replace operation, I ran into a transaction abort that resulted in the following trace: [23919.655368] WARNING: CPU: 10 PID: 30175 at fs/btrfs/extent-tree.c:9843 btrfs_create_pending_block_groups+0x15e/0x1ab [btrfs]() [23919.664742] BTRFS: Transaction aborted (error -2) [23919.665749] Modules linked in: btrfs crc32c_generic xor raid6_pq nfsd auth_rpcgss oid_registry nfs_acl nfs lockd grace fscache sunrpc loop fuse parport_pc i2c_piix4 parport psmouse acpi_cpufreq processor i2c_core evdev microcode pcspkr button serio_raw ext4 crc16 jbd2 mbcache sd_mod sg sr_mod cdrom virtio_scsi ata_generic ata_piix virtio_pci floppy virtio_ring libata e1000 virtio scsi_mod [last unloaded: btrfs] [23919.679442] CPU: 10 PID: 30175 Comm: fsstress Not tainted 4.3.0-rc5-btrfs-next-17+ #1 [23919.682392] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.8.1-0-g4adadbd-20150316_085822-nilsson.home.kraxel.org 04/01/2014 [23919.689151] 0000000000000000 ffff8804020cbb50 ffffffff812566f4 ffff8804020cbb98 [23919.692604] ffff8804020cbb88 ffffffff8104d0a6 ffffffffa03eea69 ffff88041b678a48 [23919.694230] ffff88042ac38000 ffff88041b678930 00000000fffffffe ffff8804020cbbf0 [23919.696716] Call Trace: [23919.698669] [] dump_stack+0x4e/0x79 [23919.700597] [] warn_slowpath_common+0x9f/0xb8 [23919.701958] [] ? btrfs_create_pending_block_groups+0x15e/0x1ab [btrfs] [23919.703612] [] warn_slowpath_fmt+0x48/0x50 [23919.705047] [] btrfs_create_pending_block_groups+0x15e/0x1ab [btrfs] [23919.706967] [] __btrfs_end_transaction+0x84/0x2dd [btrfs] [23919.708611] [] btrfs_end_transaction+0x10/0x12 [btrfs] [23919.710099] [] btrfs_alloc_data_chunk_ondemand+0x121/0x28b [btrfs] [23919.711970] [] btrfs_fallocate+0x7d3/0xc6d [btrfs] [23919.713602] [] ? lock_acquire+0x10d/0x194 [23919.714756] [] ? percpu_down_read+0x51/0x78 [23919.716155] [] ? __sb_start_write+0x5f/0xb0 [23919.718918] [] ? __sb_start_write+0x5f/0xb0 [23919.724170] [] vfs_fallocate+0x170/0x1ff [23919.725482] [] ioctl_preallocate+0x89/0x9b [23919.726790] [] do_vfs_ioctl+0x406/0x4e6 [23919.728428] [] ? SYSC_newfstat+0x25/0x2e [23919.729642] [] ? __fget_light+0x4d/0x71 [23919.730782] [] SyS_ioctl+0x57/0x79 [23919.731847] [] entry_SYSCALL_64_fastpath+0x12/0x6f [23919.733330] ---[ end trace 166ef301a335832a ]--- This is due to a race between device replace and chunk allocation, which the following diagram illustrates: CPU 1 CPU 2 btrfs_dev_replace_finishing() at this point dev_replace->tgtdev->devid == BTRFS_DEV_REPLACE_DEVID (0ULL) ... btrfs_start_transaction() btrfs_commit_transaction() btrfs_fallocate() btrfs_alloc_data_chunk_ondemand() btrfs_join_transaction() --> starts a new transaction do_chunk_alloc() lock fs_info->chunk_mutex btrfs_alloc_chunk() --> creates extent map for the new chunk with em->bdev->map->stripes[i]->dev->devid == X (X > 0) --> extent map is added to fs_info->mapping_tree --> initial phase of bg A allocation completes unlock fs_info->chunk_mutex lock fs_info->chunk_mutex btrfs_dev_replace_update_device_in_mapping_tree() --> iterates fs_info->mapping_tree and replaces the device in every extent map's map->stripes[] with dev_replace->tgtdev, which still has an id of 0ULL (BTRFS_DEV_REPLACE_DEVID) btrfs_end_transaction() btrfs_create_pending_block_groups() --> starts final phase of bg A creation (update device, extent, and chunk trees, etc) btrfs_finish_chunk_alloc() btrfs_update_device() --> attempts to update a device item with ID == 0ULL (BTRFS_DEV_REPLACE_DEVID) which is the current ID of bg A's em->bdev->map->stripes[i]->dev->devid --> doesn't find such item returns -ENOENT --> the device id should have been X and not 0ULL got -ENOENT from btrfs_finish_chunk_alloc() and aborts current transaction finishes setting up the target device, namely it sets tgtdev->devid to the value of srcdev->devid, which is X (and X > 0) frees the srcdev unlock fs_info->chunk_mutex So fix this by taking the device list mutex when processing the chunk's extent map stripes to update the device items. This avoids getting the wrong device id and use-after-free problems if the task finishing a chunk allocation grabs the replaced device, which is freed while the dev replace task is holding the device list mutex. This happened while running fstest btrfs/071. Signed-off-by: Filipe Manana Reviewed-by: Liu Bo --- fs/btrfs/volumes.c | 17 +++++++++++++++-- 1 file changed, 15 insertions(+), 2 deletions(-) diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c index 86124cd..f5e5e20 100644 --- a/fs/btrfs/volumes.c +++ b/fs/btrfs/volumes.c @@ -4824,20 +4824,32 @@ int btrfs_finish_chunk_alloc(struct btrfs_trans_handle *trans, goto out; } + /* + * Take the device list mutex to prevent races with the final phase of + * a device replace operation that replaces the device object associated + * with the map's stripes, because the device object's id can change + * at any time during that final phase of the device replace operation + * (dev-replace.c:btrfs_dev_replace_finishing()). + */ + mutex_lock(&chunk_root->fs_info->fs_devices->device_list_mutex); for (i = 0; i < map->num_stripes; i++) { device = map->stripes[i].dev; dev_offset = map->stripes[i].physical; ret = btrfs_update_device(trans, device); if (ret) - goto out; + break; ret = btrfs_alloc_dev_extent(trans, device, chunk_root->root_key.objectid, BTRFS_FIRST_CHUNK_TREE_OBJECTID, chunk_offset, dev_offset, stripe_size); if (ret) - goto out; + break; + } + if (ret) { + mutex_unlock(&chunk_root->fs_info->fs_devices->device_list_mutex); + goto out; } stripe = &chunk->stripe; @@ -4850,6 +4862,7 @@ int btrfs_finish_chunk_alloc(struct btrfs_trans_handle *trans, memcpy(stripe->dev_uuid, device->uuid, BTRFS_UUID_SIZE); stripe++; } + mutex_unlock(&chunk_root->fs_info->fs_devices->device_list_mutex); btrfs_set_stack_chunk_length(chunk, chunk_size); btrfs_set_stack_chunk_owner(chunk, extent_root->root_key.objectid); -- 2.7.4