| Message ID | 0cfb4c4a8ecd33b57dc0c8af2561afbc11a1fe42.1436932019.git.zhaolei@cn.fujitsu.com (mailing list archive) |
|---|---|
| State | Accepted |
| Headers | show |
On Wed, Jul 15, 2015 at 11:48:14AM +0800, Zhaolei wrote: > From: Zhao Lei <zhaolei@cn.fujitsu.com> > > Liu Bo <bo.li.liu@oracle.com> reported a lockdep warning of > delayed_iput_sem in xfstests generic/241: > [ 2061.345955] ============================================= > [ 2061.346027] [ INFO: possible recursive locking detected ] > [ 2061.346027] 4.1.0+ #268 Tainted: G W > [ 2061.346027] --------------------------------------------- > [ 2061.346027] btrfs-cleaner/3045 is trying to acquire lock: > [ 2061.346027] (&fs_info->delayed_iput_sem){++++..}, at: > [<ffffffff814063ab>] btrfs_run_delayed_iputs+0x6b/0x100 > [ 2061.346027] but task is already holding lock: > [ 2061.346027] (&fs_info->delayed_iput_sem){++++..}, at: [<ffffffff814063ab>] btrfs_run_delayed_iputs+0x6b/0x100 > [ 2061.346027] other info that might help us debug this: > [ 2061.346027] Possible unsafe locking scenario: > > [ 2061.346027] CPU0 > [ 2061.346027] ---- > [ 2061.346027] lock(&fs_info->delayed_iput_sem); > [ 2061.346027] lock(&fs_info->delayed_iput_sem); > [ 2061.346027] > *** DEADLOCK *** > It is rarely happened, about 1/400 in my test env. > > The reason is recursion of btrfs_run_delayed_iputs(): > cleaner_kthread > -> btrfs_run_delayed_iputs() *1 > -> get delayed_iput_sem lock *2 > -> iput() > -> ... > -> btrfs_commit_transaction() > -> btrfs_run_delayed_iputs() *1 > -> get delayed_iput_sem lock (dead lock) *2 > *1: recursion of btrfs_run_delayed_iputs() > *2: warning of lockdep about delayed_iput_sem > > When fs is in high stress, new iputs may added into fs_info->delayed_iputs > list when btrfs_run_delayed_iputs() is running, which cause > second btrfs_run_delayed_iputs() run into down_read(&fs_info->delayed_iput_sem) > again, and cause above lockdep warning. > > Actually, it will not cause real problem because both locks are read lock, > but to avoid lockdep warning, we can do a fix. > > Fix: > Don't do btrfs_run_delayed_iputs() in btrfs_commit_transaction() for > cleaner_kthread thread to break above recursion path. > cleaner_kthread is calling btrfs_run_delayed_iputs() explicitly in code, > and don't need to call btrfs_run_delayed_iputs() again in > btrfs_commit_transaction(), it also give us a bonus to avoid stack overflow. > > Test: > No above lockdep warning after patch in 1200 generic/241 tests. Reviewed-by: Liu Bo <bo.li.liu@oracle.com> Thanks, -liubo > > Reported-by: Liu Bo <bo.li.liu@oracle.com> > Signed-off-by: Zhao Lei <zhaolei@cn.fujitsu.com> > --- > fs/btrfs/transaction.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c > index c0f18e7..31248ad 100644 > --- a/fs/btrfs/transaction.c > +++ b/fs/btrfs/transaction.c > @@ -2152,7 +2152,8 @@ int btrfs_commit_transaction(struct btrfs_trans_handle *trans, > > kmem_cache_free(btrfs_trans_handle_cachep, trans); > > - if (current != root->fs_info->transaction_kthread) > + if (current != root->fs_info->transaction_kthread && > + current != root->fs_info->cleaner_kthread) > btrfs_run_delayed_iputs(root); > > return ret; > -- > 1.8.5.1 > > -- > To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c index c0f18e7..31248ad 100644 --- a/fs/btrfs/transaction.c +++ b/fs/btrfs/transaction.c @@ -2152,7 +2152,8 @@ int btrfs_commit_transaction(struct btrfs_trans_handle *trans, kmem_cache_free(btrfs_trans_handle_cachep, trans); - if (current != root->fs_info->transaction_kthread) + if (current != root->fs_info->transaction_kthread && + current != root->fs_info->cleaner_kthread) btrfs_run_delayed_iputs(root); return ret;