Re: [PATCH] nfsd: don't put blocked locks on LRU until after vfs_lock_file returns

["J. Bruce Fields" <bfields@fieldses.org>]

On Tue, Nov 23, 2021 at 07:22:23AM -0500, Jeff Layton wrote:
> Vasily reported a case where vfs_lock_file took a very long time to
> return (longer than a lease period). The laundromat eventually ran and
> reaped the thing and when the vfs_lock_file returned, it ended up
> accessing freed memory.

By the way, once we've called vfs_lock_file(), is there anything
preventing nfsd4_cb_notify_lock_release() from freeing nbl before we get
here?

> 
> Don't put entries onto the LRU until vfs_lock_file returns.
> 
> Reported-by: Vasily Averin <vvs@virtuozzo.com>
> Signed-off-by: Jeff Layton <jlayton@kernel.org>
> ---
>  fs/nfsd/nfs4state.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
> index bfad94c70b84..8cfef84b9355 100644
> --- a/fs/nfsd/nfs4state.c
> +++ b/fs/nfsd/nfs4state.c
> @@ -6966,10 +6966,8 @@ nfsd4_lock(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
>  	}
>  
>  	if (fl_flags & FL_SLEEP) {
> -		nbl->nbl_time = ktime_get_boottime_seconds();
>  		spin_lock(&nn->blocked_locks_lock);
>  		list_add_tail(&nbl->nbl_list, &lock_sop->lo_blocked);
> -		list_add_tail(&nbl->nbl_lru, &nn->blocked_locks_lru);
>  		spin_unlock(&nn->blocked_locks_lock);
>  	}
>  
> @@ -6982,6 +6980,10 @@ nfsd4_lock(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
>  			nn->somebody_reclaimed = true;
>  		break;
>  	case FILE_LOCK_DEFERRED:
> +		nbl->nbl_time = ktime_get_boottime_seconds();
> +		spin_lock(&nn->blocked_locks_lock);
> +		list_add_tail(&nbl->nbl_lru, &nn->blocked_locks_lru);
> +		spin_unlock(&nn->blocked_locks_lock);
>  		nbl = NULL;
>  		fallthrough;
>  	case -EAGAIN:		/* conflock holds conflicting lock */
> -- 
> 2.33.1