From 7991dbff6849f67e823b7cc0c15e5a90b0549b9f Mon Sep 17 00:00:00 2001
From: Zhihao Cheng <chengzhihao1@huawei.com>
Date: Thu, 8 Dec 2022 22:28:02 +0800
Subject: [PATCH] dm thin: Use last transaction's pmd->root when commit failed
Git-commit: 7991dbff6849f67e823b7cc0c15e5a90b0549b9f
Patch-mainline: v6.2-rc1
References: git-fixes
Recently we found a softlock up problem in dm thin pool btree lookup
code due to corrupted metadata:
Kernel panic - not syncing: softlockup: hung tasks
CPU: 7 PID: 2669225 Comm: kworker/u16:3
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996)
Workqueue: dm-thin do_worker [dm_thin_pool]
Call Trace:
<IRQ>
dump_stack+0x9c/0xd3
panic+0x35d/0x6b9
watchdog_timer_fn.cold+0x16/0x25
__run_hrtimer+0xa2/0x2d0
</IRQ>
RIP: 0010:__relink_lru+0x102/0x220 [dm_bufio]
__bufio_new+0x11f/0x4f0 [dm_bufio]
new_read+0xa3/0x1e0 [dm_bufio]
dm_bm_read_lock+0x33/0xd0 [dm_persistent_data]
ro_step+0x63/0x100 [dm_persistent_data]
btree_lookup_raw.constprop.0+0x44/0x220 [dm_persistent_data]
dm_btree_lookup+0x16f/0x210 [dm_persistent_data]
dm_thin_find_block+0x12c/0x210 [dm_thin_pool]
__process_bio_read_only+0xc5/0x400 [dm_thin_pool]
process_thin_deferred_bios+0x1a4/0x4a0 [dm_thin_pool]
process_one_work+0x3c5/0x730
Following process may generate a broken btree mixed with fresh and
stale btree nodes, which could get dm thin trapped in an infinite loop
while looking up data block:
Transaction 1: pmd->root = A, A->B->C // One path in btree
pmd->root = X, X->Y->Z // Copy-up
Transaction 2: X,Z is updated on disk, Y write failed.
// Commit failed, dm thin becomes read-only.
process_bio_read_only
dm_thin_find_block
__find_block
dm_btree_lookup(pmd->root)
The pmd->root points to a broken btree, Y may contain stale node
pointing to any block, for example X, which gets dm thin trapped into
a dead loop while looking up Z.
Fix this by setting pmd->root in __open_metadata(), so that dm thin
will use the last transaction's pmd->root if commit failed.
Fetch a reproducer in [Link].
Linke: https://bugzilla.kernel.org/show_bug.cgi?id=216790
Cc: stable@vger.kernel.org
Fixes: 991d9fa02da0 ("dm: add thin provisioning target")
Signed-off-by: Zhihao Cheng <chengzhihao1@huawei.com>
Acked-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@kernel.org>
Signed-off-by: Coly Li <colyli@suse.de>
---
drivers/md/dm-thin-metadata.c | 9 +++++++++
1 file changed, 9 insertions(+)
diff --git a/drivers/md/dm-thin-metadata.c b/drivers/md/dm-thin-metadata.c
index 1a62226ac34e..6bcc4c4786d8 100644
--- a/drivers/md/dm-thin-metadata.c
+++ b/drivers/md/dm-thin-metadata.c
@@ -724,6 +724,15 @@ static int __open_metadata(struct dm_pool_metadata *pmd)
goto bad_cleanup_data_sm;
}
+ /*
+ * For pool metadata opening process, root setting is redundant
+ * because it will be set again in __begin_transaction(). But dm
+ * pool aborting process really needs to get last transaction's
+ * root to avoid accessing broken btree.
+ */
+ pmd->root = le64_to_cpu(disk_super->data_mapping_root);
+ pmd->details_root = le64_to_cpu(disk_super->device_details_root);
+
__setup_btree_details(pmd);
dm_bm_unlock(sblock);
--
2.35.3