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authorFilipe Manana <fdmanana@suse.com>2019-09-10 15:26:49 +0100
committerDavid Sterba <dsterba@suse.com>2019-09-12 13:37:19 +0200
commit410f954cb1d1c79ae485dd83a175f21954fd87cd (patch)
tree3bc8a3210514d677064ee3c8c0522a7565ca6194
parent07301df7d2fc220d3de5f7ad804dcb941400cb00 (diff)
Btrfs: fix assertion failure during fsync and use of stale transaction
Sometimes when fsync'ing a file we need to log that other inodes exist and when we need to do that we acquire a reference on the inodes and then drop that reference using iput() after logging them. That generally is not a problem except if we end up doing the final iput() (dropping the last reference) on the inode and that inode has a link count of 0, which can happen in a very short time window if the logging path gets a reference on the inode while it's being unlinked. In that case we end up getting the eviction callback, btrfs_evict_inode(), invoked through the iput() call chain which needs to drop all of the inode's items from its subvolume btree, and in order to do that, it needs to join a transaction at the helper function evict_refill_and_join(). However because the task previously started a transaction at the fsync handler, btrfs_sync_file(), it has current->journal_info already pointing to a transaction handle and therefore evict_refill_and_join() will get that transaction handle from btrfs_join_transaction(). From this point on, two different problems can happen: 1) evict_refill_and_join() will often change the transaction handle's block reserve (->block_rsv) and set its ->bytes_reserved field to a value greater than 0. If evict_refill_and_join() never commits the transaction, the eviction handler ends up decreasing the reference count (->use_count) of the transaction handle through the call to btrfs_end_transaction(), and after that point we have a transaction handle with a NULL ->block_rsv (which is the value prior to the transaction join from evict_refill_and_join()) and a ->bytes_reserved value greater than 0. If after the eviction/iput completes the inode logging path hits an error or it decides that it must fallback to a transaction commit, the btrfs fsync handle, btrfs_sync_file(), gets a non-zero value from btrfs_log_dentry_safe(), and because of that non-zero value it tries to commit the transaction using a handle with a NULL ->block_rsv and a non-zero ->bytes_reserved value. This makes the transaction commit hit an assertion failure at btrfs_trans_release_metadata() because ->bytes_reserved is not zero but the ->block_rsv is NULL. The produced stack trace for that is like the following: [192922.917158] assertion failed: !trans->bytes_reserved, file: fs/btrfs/transaction.c, line: 816 [192922.917553] ------------[ cut here ]------------ [192922.917922] kernel BUG at fs/btrfs/ctree.h:3532! [192922.918310] invalid opcode: 0000 [#1] SMP DEBUG_PAGEALLOC PTI [192922.918666] CPU: 2 PID: 883 Comm: fsstress Tainted: G W 5.1.4-btrfs-next-47 #1 [192922.919035] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.11.2-0-gf9626ccb91-prebuilt.qemu-project.org 04/01/2014 [192922.919801] RIP: 0010:assfail.constprop.25+0x18/0x1a [btrfs] (...) [192922.920925] RSP: 0018:ffffaebdc8a27da8 EFLAGS: 00010286 [192922.921315] RAX: 0000000000000051 RBX: ffff95c9c16a41c0 RCX: 0000000000000000 [192922.921692] RDX: 0000000000000000 RSI: ffff95cab6b16838 RDI: ffff95cab6b16838 [192922.922066] RBP: ffff95c9c16a41c0 R08: 0000000000000000 R09: 0000000000000000 [192922.922442] R10: ffffaebdc8a27e70 R11: 0000000000000000 R12: ffff95ca731a0980 [192922.922820] R13: 0000000000000000 R14: ffff95ca84c73338 R15: ffff95ca731a0ea8 [192922.923200] FS: 00007f337eda4e80(0000) GS:ffff95cab6b00000(0000) knlGS:0000000000000000 [192922.923579] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [192922.923948] CR2: 00007f337edad000 CR3: 00000001e00f6002 CR4: 00000000003606e0 [192922.924329] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 [192922.924711] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 [192922.925105] Call Trace: [192922.925505] btrfs_trans_release_metadata+0x10c/0x170 [btrfs] [192922.925911] btrfs_commit_transaction+0x3e/0xaf0 [btrfs] [192922.926324] btrfs_sync_file+0x44c/0x490 [btrfs] [192922.926731] do_fsync+0x38/0x60 [192922.927138] __x64_sys_fdatasync+0x13/0x20 [192922.927543] do_syscall_64+0x60/0x1c0 [192922.927939] entry_SYSCALL_64_after_hwframe+0x49/0xbe (...) [192922.934077] ---[ end trace f00808b12068168f ]--- 2) If evict_refill_and_join() decides to commit the transaction, it will be able to do it, since the nested transaction join only increments the transaction handle's ->use_count reference counter and it does not prevent the transaction from getting committed. This means that after eviction completes, the fsync logging path will be using a transaction handle that refers to an already committed transaction. What happens when using such a stale transaction can be unpredictable, we are at least having a use-after-free on the transaction handle itself, since the transaction commit will call kmem_cache_free() against the handle regardless of its ->use_count value, or we can end up silently losing all the updates to the log tree after that iput() in the logging path, or using a transaction handle that in the meanwhile was allocated to another task for a new transaction, etc, pretty much unpredictable what can happen. In order to fix both of them, instead of using iput() during logging, use btrfs_add_delayed_iput(), so that the logging path of fsync never drops the last reference on an inode, that step is offloaded to a safe context (usually the cleaner kthread). The assertion failure issue was sporadically triggered by the test case generic/475 from fstests, which loads the dm error target while fsstress is running, which lead to fsync failing while logging inodes with -EIO errors and then trying later to commit the transaction, triggering the assertion failure. CC: stable@vger.kernel.org # 4.4+ Reviewed-by: Josef Bacik <josef@toxicpanda.com> Signed-off-by: Filipe Manana <fdmanana@suse.com> Signed-off-by: David Sterba <dsterba@suse.com>
-rw-r--r--fs/btrfs/tree-log.c16
1 files changed, 8 insertions, 8 deletions
diff --git a/fs/btrfs/tree-log.c b/fs/btrfs/tree-log.c
index 6c8297bcfeb7..1bfd7e34f31e 100644
--- a/fs/btrfs/tree-log.c
+++ b/fs/btrfs/tree-log.c
@@ -4985,7 +4985,7 @@ static int log_conflicting_inodes(struct btrfs_trans_handle *trans,
BTRFS_I(inode),
LOG_OTHER_INODE_ALL,
0, LLONG_MAX, ctx);
- iput(inode);
+ btrfs_add_delayed_iput(inode);
}
}
continue;
@@ -5000,7 +5000,7 @@ static int log_conflicting_inodes(struct btrfs_trans_handle *trans,
ret = btrfs_log_inode(trans, root, BTRFS_I(inode),
LOG_OTHER_INODE, 0, LLONG_MAX, ctx);
if (ret) {
- iput(inode);
+ btrfs_add_delayed_iput(inode);
continue;
}
@@ -5009,7 +5009,7 @@ static int log_conflicting_inodes(struct btrfs_trans_handle *trans,
key.offset = 0;
ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
if (ret < 0) {
- iput(inode);
+ btrfs_add_delayed_iput(inode);
continue;
}
@@ -5056,7 +5056,7 @@ static int log_conflicting_inodes(struct btrfs_trans_handle *trans,
}
path->slots[0]++;
}
- iput(inode);
+ btrfs_add_delayed_iput(inode);
}
return ret;
@@ -5689,7 +5689,7 @@ process_leaf:
}
if (btrfs_inode_in_log(BTRFS_I(di_inode), trans->transid)) {
- iput(di_inode);
+ btrfs_add_delayed_iput(di_inode);
break;
}
@@ -5701,7 +5701,7 @@ process_leaf:
if (!ret &&
btrfs_must_commit_transaction(trans, BTRFS_I(di_inode)))
ret = 1;
- iput(di_inode);
+ btrfs_add_delayed_iput(di_inode);
if (ret)
goto next_dir_inode;
if (ctx->log_new_dentries) {
@@ -5848,7 +5848,7 @@ static int btrfs_log_all_parents(struct btrfs_trans_handle *trans,
if (!ret && ctx && ctx->log_new_dentries)
ret = log_new_dir_dentries(trans, root,
BTRFS_I(dir_inode), ctx);
- iput(dir_inode);
+ btrfs_add_delayed_iput(dir_inode);
if (ret)
goto out;
}
@@ -5891,7 +5891,7 @@ static int log_new_ancestors(struct btrfs_trans_handle *trans,
ret = btrfs_log_inode(trans, root, BTRFS_I(inode),
LOG_INODE_EXISTS,
0, LLONG_MAX, ctx);
- iput(inode);
+ btrfs_add_delayed_iput(inode);
if (ret)
return ret;