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authorQu Wenruo <wqu@suse.com>2018-04-13 06:32:47 +0800
committerDavid Sterba <dsterba@suse.com>2018-04-13 16:16:15 +0200
commit5d41be6f702f19f72db816c17175caf9dbdcdfa6 (patch)
treedca5362157e2dd8a235e0d99c2b95f09151aba05
parent852eb3aeeaf65f175f15c7af6a31aeffc050d659 (diff)
btrfs: Only check first key for committed tree blocks
When looping btrfs/074 with many cpus (>= 8), it's possible to trigger kernel warning due to first key verification: [ 4239.523446] WARNING: CPU: 5 PID: 2381 at fs/btrfs/disk-io.c:460 btree_read_extent_buffer_pages+0x1ad/0x210 [ 4239.523830] Modules linked in: [ 4239.524630] RIP: 0010:btree_read_extent_buffer_pages+0x1ad/0x210 [ 4239.527101] Call Trace: [ 4239.527251] read_tree_block+0x42/0x70 [ 4239.527434] read_node_slot+0xd2/0x110 [ 4239.527632] push_leaf_right+0xad/0x1b0 [ 4239.527809] split_leaf+0x4ea/0x700 [ 4239.527988] ? leaf_space_used+0xbc/0xe0 [ 4239.528192] ? btrfs_set_lock_blocking_rw+0x99/0xb0 [ 4239.528416] btrfs_search_slot+0x8cc/0xa40 [ 4239.528605] btrfs_insert_empty_items+0x71/0xc0 [ 4239.528798] __btrfs_run_delayed_refs+0xa98/0x1680 [ 4239.529013] btrfs_run_delayed_refs+0x10b/0x1b0 [ 4239.529205] btrfs_commit_transaction+0x33/0xaf0 [ 4239.529445] ? start_transaction+0xa8/0x4f0 [ 4239.529630] btrfs_alloc_data_chunk_ondemand+0x1b0/0x4e0 [ 4239.529833] btrfs_check_data_free_space+0x54/0xa0 [ 4239.530045] btrfs_delalloc_reserve_space+0x25/0x70 [ 4239.531907] btrfs_direct_IO+0x233/0x3d0 [ 4239.532098] generic_file_direct_write+0xcb/0x170 [ 4239.532296] btrfs_file_write_iter+0x2bb/0x5f4 [ 4239.532491] aio_write+0xe2/0x180 [ 4239.532669] ? lock_acquire+0xac/0x1e0 [ 4239.532839] ? __might_fault+0x3e/0x90 [ 4239.533032] do_io_submit+0x594/0x860 [ 4239.533223] ? do_io_submit+0x594/0x860 [ 4239.533398] SyS_io_submit+0x10/0x20 [ 4239.533560] ? SyS_io_submit+0x10/0x20 [ 4239.533729] do_syscall_64+0x75/0x1d0 [ 4239.533979] entry_SYSCALL_64_after_hwframe+0x42/0xb7 [ 4239.534182] RIP: 0033:0x7f8519741697 The problem here is, at btree_read_extent_buffer_pages() we don't have acquired read/write lock on that extent buffer, only basic info like level/bytenr is reliable. So race condition leads to such false alert. However in current call site, it's impossible to acquire proper lock without race window. To fix the problem, we only verify first key for committed tree blocks (whose generation is no larger than fs_info->last_trans_committed), so the content of such tree blocks will not change and there is no need to get read/write lock. Reported-by: Nikolay Borisov <nborisov@suse.com> Fixes: 581c1760415c ("btrfs: Validate child tree block's level and first key") Signed-off-by: Qu Wenruo <wqu@suse.com> Signed-off-by: David Sterba <dsterba@suse.com>
-rw-r--r--fs/btrfs/disk-io.c8
1 files changed, 8 insertions, 0 deletions
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 74cbc342b29a..4ac8b1d21baf 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -436,6 +436,14 @@ static int verify_level_key(struct btrfs_fs_info *fs_info,
if (!first_key)
return 0;
+ /*
+ * For live tree block (new tree blocks in current transaction),
+ * we need proper lock context to avoid race, which is impossible here.
+ * So we only checks tree blocks which is read from disk, whose
+ * generation <= fs_info->last_trans_committed.
+ */
+ if (btrfs_header_generation(eb) > fs_info->last_trans_committed)
+ return 0;
if (found_level)
btrfs_node_key_to_cpu(eb, &found_key, 0);
else