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authorFilipe Manana2015-06-11 01:58:53 +0200
committerChris Mason2015-06-30 23:36:46 +0200
commit67c5e7d464bc466471b05e027abe8a6b29687ebd (patch)
tree20f6112838a0957f6c05e5100aabb581606ea20d /fs/btrfs/volumes.c
parentbtrfs: add error handling for scrub_workers_get() (diff)
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Btrfs: fix race between balance and unused block group deletion
We have a race between deleting an unused block group and balancing the same block group that leads to an assertion failure/BUG(), producing the following trace: [181631.208236] BTRFS: assertion failed: 0, file: fs/btrfs/volumes.c, line: 2622 [181631.220591] ------------[ cut here ]------------ [181631.222959] kernel BUG at fs/btrfs/ctree.h:4062! [181631.223932] invalid opcode: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC [181631.224566] Modules linked in: btrfs dm_flakey dm_mod crc32c_generic xor raid6_pq nfsd auth_rpcgss oid_registry nfs_acl nfs lockd grace fscache sunrpc loop fuse acpi_cpufreq parpor$ [181631.224566] CPU: 8 PID: 17451 Comm: btrfs Tainted: G W 4.1.0-rc5-btrfs-next-10+ #1 [181631.224566] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.8.1-0-g4adadbd-20150316_085822-nilsson.home.kraxel.org 04/01/2014 [181631.224566] task: ffff880127e09590 ti: ffff8800b5824000 task.ti: ffff8800b5824000 [181631.224566] RIP: 0010:[<ffffffffa03f19f6>] [<ffffffffa03f19f6>] assfail.constprop.50+0x1e/0x20 [btrfs] [181631.224566] RSP: 0018:ffff8800b5827ae8 EFLAGS: 00010246 [181631.224566] RAX: 0000000000000040 RBX: ffff8800109fc218 RCX: ffffffff81095dce [181631.224566] RDX: 0000000000005124 RSI: ffffffff81464819 RDI: 00000000ffffffff [181631.224566] RBP: ffff8800b5827ae8 R08: 0000000000000001 R09: 0000000000000000 [181631.224566] R10: 0000000000000000 R11: 0000000000000000 R12: ffff8800109fc200 [181631.224566] R13: ffff880020095000 R14: ffff8800b1a13f38 R15: ffff880020095000 [181631.224566] FS: 00007f70ca0b0c80(0000) GS:ffff88013ec00000(0000) knlGS:0000000000000000 [181631.224566] CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b [181631.224566] CR2: 00007f2872ab6e68 CR3: 00000000a717c000 CR4: 00000000000006e0 [181631.224566] Stack: [181631.224566] ffff8800b5827ba8 ffffffffa03f3916 ffff8800b5827b38 ffffffffa03d080e [181631.224566] ffffffffa03d1423 ffff880020095000 ffff88001233c000 0000000000000001 [181631.224566] ffff880020095000 ffff8800b1a13f38 0000000a69c00000 0000000000000000 [181631.224566] Call Trace: [181631.224566] [<ffffffffa03f3916>] btrfs_remove_chunk+0xa4/0x6bb [btrfs] [181631.224566] [<ffffffffa03d080e>] ? join_transaction.isra.8+0xb9/0x3ba [btrfs] [181631.224566] [<ffffffffa03d1423>] ? wait_current_trans.isra.13+0x22/0xfc [btrfs] [181631.224566] [<ffffffffa03f3fbc>] btrfs_relocate_chunk.isra.29+0x8f/0xa7 [btrfs] [181631.224566] [<ffffffffa03f54df>] btrfs_balance+0xaa4/0xc52 [btrfs] [181631.224566] [<ffffffffa03fd388>] btrfs_ioctl_balance+0x23f/0x2b0 [btrfs] [181631.224566] [<ffffffff810872f9>] ? trace_hardirqs_on+0xd/0xf [181631.224566] [<ffffffffa04019a3>] btrfs_ioctl+0xfe2/0x2220 [btrfs] [181631.224566] [<ffffffff812603ed>] ? __this_cpu_preempt_check+0x13/0x15 [181631.224566] [<ffffffff81084669>] ? arch_local_irq_save+0x9/0xc [181631.224566] [<ffffffff81138def>] ? handle_mm_fault+0x834/0xcd2 [181631.224566] [<ffffffff81138def>] ? handle_mm_fault+0x834/0xcd2 [181631.224566] [<ffffffff8103e48c>] ? __do_page_fault+0x211/0x424 [181631.224566] [<ffffffff811755e6>] do_vfs_ioctl+0x3c6/0x479 (...) The sequence of steps leading to this are: CPU 0 CPU 1 btrfs_balance() btrfs_relocate_chunk() btrfs_relocate_block_group(bg X) btrfs_lookup_block_group(bg X) cleaner_kthread locks fs_info->cleaner_mutex btrfs_delete_unused_bgs() finds bg X, which became unused in the previous transaction checks bg X ->ro == 0, so it proceeds sets bg X ->ro to 1 (btrfs_set_block_group_ro(bg X)) blocks on fs_info->cleaner_mutex btrfs_remove_chunk(bg X) unlocks fs_info->cleaner_mutex acquires fs_info->cleaner_mutex relocate_block_group() --> does nothing, no extents found in the extent tree from bg X unlocks fs_info->cleaner_mutex btrfs_relocate_block_group(bg X) returns btrfs_remove_chunk(bg X) extent map not found --> ASSERT(0) Fix this by using a new mutex to make sure these 2 operations, block group relocation and removal, are serialized. This issue is reproducible by running fstests generic/038 (which stresses chunk allocation and automatic removal of unused block groups) together with the following balance loop: while true; do btrfs balance start -dusage=0 <mountpoint> ; done Signed-off-by: Filipe Manana <fdmanana@suse.com> Signed-off-by: Chris Mason <clm@fb.com>
Diffstat (limited to 'fs/btrfs/volumes.c')
-rw-r--r--fs/btrfs/volumes.c48
1 files changed, 43 insertions, 5 deletions
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index d4cd4059bded..9b95503ddd00 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -2766,6 +2766,20 @@ static int btrfs_relocate_chunk(struct btrfs_root *root,
root = root->fs_info->chunk_root;
extent_root = root->fs_info->extent_root;
+ /*
+ * Prevent races with automatic removal of unused block groups.
+ * After we relocate and before we remove the chunk with offset
+ * chunk_offset, automatic removal of the block group can kick in,
+ * resulting in a failure when calling btrfs_remove_chunk() below.
+ *
+ * Make sure to acquire this mutex before doing a tree search (dev
+ * or chunk trees) to find chunks. Otherwise the cleaner kthread might
+ * call btrfs_remove_chunk() (through btrfs_delete_unused_bgs()) after
+ * we release the path used to search the chunk/dev tree and before
+ * the current task acquires this mutex and calls us.
+ */
+ ASSERT(mutex_is_locked(&root->fs_info->delete_unused_bgs_mutex));
+
ret = btrfs_can_relocate(extent_root, chunk_offset);
if (ret)
return -ENOSPC;
@@ -2814,13 +2828,18 @@ again:
key.type = BTRFS_CHUNK_ITEM_KEY;
while (1) {
+ mutex_lock(&root->fs_info->delete_unused_bgs_mutex);
ret = btrfs_search_slot(NULL, chunk_root, &key, path, 0, 0);
- if (ret < 0)
+ if (ret < 0) {
+ mutex_unlock(&root->fs_info->delete_unused_bgs_mutex);
goto error;
+ }
BUG_ON(ret == 0); /* Corruption */
ret = btrfs_previous_item(chunk_root, path, key.objectid,
key.type);
+ if (ret)
+ mutex_unlock(&root->fs_info->delete_unused_bgs_mutex);
if (ret < 0)
goto error;
if (ret > 0)
@@ -2843,6 +2862,7 @@ again:
else
BUG_ON(ret);
}
+ mutex_unlock(&root->fs_info->delete_unused_bgs_mutex);
if (found_key.offset == 0)
break;
@@ -3299,9 +3319,12 @@ again:
goto error;
}
+ mutex_lock(&fs_info->delete_unused_bgs_mutex);
ret = btrfs_search_slot(NULL, chunk_root, &key, path, 0, 0);
- if (ret < 0)
+ if (ret < 0) {
+ mutex_unlock(&fs_info->delete_unused_bgs_mutex);
goto error;
+ }
/*
* this shouldn't happen, it means the last relocate
@@ -3313,6 +3336,7 @@ again:
ret = btrfs_previous_item(chunk_root, path, 0,
BTRFS_CHUNK_ITEM_KEY);
if (ret) {
+ mutex_unlock(&fs_info->delete_unused_bgs_mutex);
ret = 0;
break;
}
@@ -3321,8 +3345,10 @@ again:
slot = path->slots[0];
btrfs_item_key_to_cpu(leaf, &found_key, slot);
- if (found_key.objectid != key.objectid)
+ if (found_key.objectid != key.objectid) {
+ mutex_unlock(&fs_info->delete_unused_bgs_mutex);
break;
+ }
chunk = btrfs_item_ptr(leaf, slot, struct btrfs_chunk);
@@ -3335,10 +3361,13 @@ again:
ret = should_balance_chunk(chunk_root, leaf, chunk,
found_key.offset);
btrfs_release_path(path);
- if (!ret)
+ if (!ret) {
+ mutex_unlock(&fs_info->delete_unused_bgs_mutex);
goto loop;
+ }
if (counting) {
+ mutex_unlock(&fs_info->delete_unused_bgs_mutex);
spin_lock(&fs_info->balance_lock);
bctl->stat.expected++;
spin_unlock(&fs_info->balance_lock);
@@ -3348,6 +3377,7 @@ again:
ret = btrfs_relocate_chunk(chunk_root,
found_key.objectid,
found_key.offset);
+ mutex_unlock(&fs_info->delete_unused_bgs_mutex);
if (ret && ret != -ENOSPC)
goto error;
if (ret == -ENOSPC) {
@@ -4087,11 +4117,16 @@ again:
key.type = BTRFS_DEV_EXTENT_KEY;
do {
+ mutex_lock(&root->fs_info->delete_unused_bgs_mutex);
ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
- if (ret < 0)
+ if (ret < 0) {
+ mutex_unlock(&root->fs_info->delete_unused_bgs_mutex);
goto done;
+ }
ret = btrfs_previous_item(root, path, 0, key.type);
+ if (ret)
+ mutex_unlock(&root->fs_info->delete_unused_bgs_mutex);
if (ret < 0)
goto done;
if (ret) {
@@ -4105,6 +4140,7 @@ again:
btrfs_item_key_to_cpu(l, &key, path->slots[0]);
if (key.objectid != device->devid) {
+ mutex_unlock(&root->fs_info->delete_unused_bgs_mutex);
btrfs_release_path(path);
break;
}
@@ -4113,6 +4149,7 @@ again:
length = btrfs_dev_extent_length(l, dev_extent);
if (key.offset + length <= new_size) {
+ mutex_unlock(&root->fs_info->delete_unused_bgs_mutex);
btrfs_release_path(path);
break;
}
@@ -4122,6 +4159,7 @@ again:
btrfs_release_path(path);
ret = btrfs_relocate_chunk(root, chunk_objectid, chunk_offset);
+ mutex_unlock(&root->fs_info->delete_unused_bgs_mutex);
if (ret && ret != -ENOSPC)
goto done;
if (ret == -ENOSPC)