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btrfs: fix races on root_log_ctx lists 

btrfs_remove_all_log_ctxs takes a shortcut where it avoids walking the
list because it knows all of the waiters are patiently waiting for the
commit to finish.

But, there's a small race where btrfs_sync_log can remove itself from
the list if it finds a log commit is already done.  Also, it uses
list_del_init() to remove itself from the list, but there's no way to
know if btrfs_remove_all_log_ctxs has already run, so we don't know for
sure if it is safe to call list_del_init().

This gets rid of all the shortcuts for btrfs_remove_all_log_ctxs(), and
just calls it with the proper locking.

This is part two of the corruption fixed by cbd60aa7cd.  I should have
done this in the first place, but convinced myself the optimizations were
safe.  A 12 hour run of dbench 2048 will eventually trigger a list debug
WARN_ON for the list_del_init() in btrfs_sync_log().

Fixes: d1433debe7
Reported-by: Dave Jones <davej@codemonkey.org.uk>
cc: stable@vger.kernel.org # 3.15+
Signed-off-by: Chris Mason <clm@fb.com>
This commit is contained in:
Chris Mason 2016-10-27 10:42:20 -07:00
parent 112a3edf4b
commit 570dd45042
1 changed files with 6 additions and 14 deletions
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20
fs/btrfs/tree-log.c
View File

@ -2713,14 +2713,12 @@ static inline void btrfs_remove_all_log_ctxs(struct btrfs_root *root,
int index, int error)
{
struct btrfs_log_ctx *ctx;
struct btrfs_log_ctx *safe;
if (!error) {
INIT_LIST_HEAD(&root->log_ctxs[index]);
return;
}
list_for_each_entry(ctx, &root->log_ctxs[index], list)
list_for_each_entry_safe(ctx, safe, &root->log_ctxs[index], list) {
list_del_init(&ctx->list);
ctx->log_ret = error;
}
INIT_LIST_HEAD(&root->log_ctxs[index]);
}
@ -2961,13 +2959,9 @@ int btrfs_sync_log(struct btrfs_trans_handle *trans,
mutex_unlock(&root->log_mutex);
out_wake_log_root:
/*
* We needn't get log_mutex here because we are sure all
* the other tasks are blocked.
*/
mutex_lock(&log_root_tree->log_mutex);
btrfs_remove_all_log_ctxs(log_root_tree, index2, ret);
mutex_lock(&log_root_tree->log_mutex);
log_root_tree->log_transid_committed++;
atomic_set(&log_root_tree->log_commit[index2], 0);
mutex_unlock(&log_root_tree->log_mutex);
@ -2978,10 +2972,8 @@ int btrfs_sync_log(struct btrfs_trans_handle *trans,
if (waitqueue_active(&log_root_tree->log_commit_wait[index2]))
wake_up(&log_root_tree->log_commit_wait[index2]);
out:
/* See above. */
btrfs_remove_all_log_ctxs(root, index1, ret);
mutex_lock(&root->log_mutex);
btrfs_remove_all_log_ctxs(root, index1, ret);
root->log_transid_committed++;
atomic_set(&root->log_commit[index1], 0);
mutex_unlock(&root->log_mutex);