Re: [PATCH] nfsd: put dl_stid if fail to queue dl_recall

[Jeff Layton <jlayton@kernel.org>]

On Thu, 2025-02-13 at 15:25 +0800, Li Lingfeng wrote:
> Before calling nfsd4_run_cb to queue dl_recall to the callback_wq, we
> increment the reference count of dl_stid.
> We expect that after the corresponding work_struct is processed, the
> reference count of dl_stid will be decremented through the callback
> function nfsd4_cb_recall_release.
> However, if the call to nfsd4_run_cb fails, the incremented reference
> count of dl_stid will not be decremented correspondingly, leading to the
> following nfs4_stid leak:
> unreferenced object 0xffff88812067b578 (size 344):
>   comm "nfsd", pid 2761, jiffies 4295044002 (age 5541.241s)
>   hex dump (first 32 bytes):
>     01 00 00 00 6b 6b 6b 6b b8 02 c0 e2 81 88 ff ff  ....kkkk........
>     00 6b 6b 6b 6b 6b 6b 6b 00 00 00 00 ad 4e ad de  .kkkkkkk.....N..
>   backtrace:
>     kmem_cache_alloc+0x4b9/0x700
>     nfsd4_process_open1+0x34/0x300
>     nfsd4_open+0x2d1/0x9d0
>     nfsd4_proc_compound+0x7a2/0xe30
>     nfsd_dispatch+0x241/0x3e0
>     svc_process_common+0x5d3/0xcc0
>     svc_process+0x2a3/0x320
>     nfsd+0x180/0x2e0
>     kthread+0x199/0x1d0
>     ret_from_fork+0x30/0x50
>     ret_from_fork_asm+0x1b/0x30
> unreferenced object 0xffff8881499f4d28 (size 368):
>   comm "nfsd", pid 2761, jiffies 4295044005 (age 5541.239s)
>   hex dump (first 32 bytes):
>     01 00 00 00 00 00 00 00 30 4d 9f 49 81 88 ff ff  ........0M.I....
>     30 4d 9f 49 81 88 ff ff 20 00 00 00 01 00 00 00  0M.I.... .......
>   backtrace:
>     kmem_cache_alloc+0x4b9/0x700
>     nfs4_alloc_stid+0x29/0x210
>     alloc_init_deleg+0x92/0x2e0
>     nfs4_set_delegation+0x284/0xc00
>     nfs4_open_delegation+0x216/0x3f0
>     nfsd4_process_open2+0x2b3/0xee0
>     nfsd4_open+0x770/0x9d0
>     nfsd4_proc_compound+0x7a2/0xe30
>     nfsd_dispatch+0x241/0x3e0
>     svc_process_common+0x5d3/0xcc0
>     svc_process+0x2a3/0x320
>     nfsd+0x180/0x2e0
>     kthread+0x199/0x1d0
>     ret_from_fork+0x30/0x50
>     ret_from_fork_asm+0x1b/0x30
> Fix it by checking the result of nfsd4_run_cb and call nfs4_put_stid if
> fail to queue dl_recall.
> 
> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> Signed-off-by: Li Lingfeng <lilingfeng3@huawei.com>
> ---
>  fs/nfsd/nfs4state.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
> index 153eeea2c7c9..0ccb87be47b7 100644
> --- a/fs/nfsd/nfs4state.c
> +++ b/fs/nfsd/nfs4state.c
> @@ -5414,6 +5414,7 @@ static const struct nfsd4_callback_ops nfsd4_cb_recall_ops = {
>  
>  static void nfsd_break_one_deleg(struct nfs4_delegation *dp)
>  {
> +	bool queued;
>  	/*
>  	 * We're assuming the state code never drops its reference
>  	 * without first removing the lease.  Since we're in this lease
> @@ -5422,7 +5423,10 @@ static void nfsd_break_one_deleg(struct nfs4_delegation *dp)
>  	 * we know it's safe to take a reference.
>  	 */
>  	refcount_inc(&dp->dl_stid.sc_count);
> -	WARN_ON_ONCE(!nfsd4_run_cb(&dp->dl_recall));
> +	queued = nfsd4_run_cb(&dp->dl_recall);
> +	WARN_ON_ONCE(!queued);
> +	if (!queued)
> +		nfs4_put_stid(&dp->dl_stid);
>  }
>  
>  /* Called from break_lease() with flc_lock held. */


Have you actually seen the WARN_ON_ONCE() pop under normal usage, or
was the problem you reproduced done via fault injection?

Unfortunately, this won't work. nfsd_break_one_deleg() is called from
the ->break_lease callback with the flc->flc_lock held, and
nfs4_put_stid can sleep in the sc_free callbacks.
-- 
Jeff Layton <jlayton@kernel.org>