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

[Li Lingfeng <lilingfeng3@huawei.com>]

在 2025/2/13 20:34, Jeff Layton 写道:
> On Thu, 2025-02-13 at 20:28 +0800, Li Lingfeng wrote:
>> 在 2025/2/13 19:49, Jeff Layton 写道:
>>> 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?
>> Hi,
>>
>> I add mdelay for cb_work before processing it and add msleep in
>> nfs_do_return_delegation to reproduce it.
>>
>> --- a/fs/nfsd/nfs4state.c
>> +++ b/fs/nfsd/nfs4state.c
>> @@ -1188,6 +1188,8 @@ alloc_init_deleg(struct nfs4_client *clp, struct
>> nfs4_file *fp,
>>        dp->dl_recalled = false;
>>        nfsd4_init_cb(&dp->dl_recall, dp->dl_stid.sc_client,
>>                  &nfsd4_cb_recall_ops, NFSPROC4_CLNT_CB_RECALL);
>> +    dp->dl_recall.cb_work.debug_flag = 0x1234;
>> +    printk("%s init work func %px\n", __func__,
>> dp->dl_recall.cb_work.func);
>>        get_nfs4_file(fp);
>>        dp->dl_stid.sc_file = fp;
>>        return dp;
>>
>> --- a/kernel/workqueue.c
>> +++ b/kernel/workqueue.c
>> @@ -2708,6 +2708,12 @@ static void process_scheduled_works(struct worker
>> *worker)
>>                worker->pool->watchdog_ts = jiffies;
>>                first = false;
>>            }
>> +        if (work->debug_flag == 0x1234) {
>> +            printk("%s func %px\n", __func__, work->func);
>> +            printk("%s delay before clear pending...\n", __func__);
>> +            mdelay(10 * 1000);
>> +            printk("%s delay done\n", __func__);
>> +        }
>>            process_one_work(worker, work);
>>        }
>>    }
>>
>> --- a/fs/nfs/delegation.c
>> +++ b/fs/nfs/delegation.c
>> @@ -263,6 +263,15 @@ static int nfs_do_return_delegation(struct inode
>> *inode, struct nfs_delegation *
>>        const struct cred *cred;
>>        int res = 0;
>>
>> +    printk("sleep before deleg return...\n");
>> +    while (1) {
>> +        ifdebug(PROC)
>> +            msleep(10 * 1000);
>> +        else
>> +            break;
>> +    }
>> +    printk("sleep done\n");
>> +
>>        if (!test_bit(NFS_DELEGATION_REVOKED, &delegation-flags)) {
>>            spin_lock(&delegation->lock);
>>            cred = get_cred(delegation->cred);
>>
>>> 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.
>> Are you referring to nfs4_free_deleg? I didn't quite see where it might
>> sleep. Could you please explain it to me?
>>
> I stand corrected. nfs4_free_deleg() won't sleep, but
> nfs4_free_lock_stateid() can. In this case, you know that this is a
> deleg stateid, so this should actually be safe after all.
>
> If you do this though, please add a comment to nfs4_free_deleg()
> mentioning that it mustn't ever sleep, since it can be called from that
> context.
Thank you for your advice, I will send v2 soon.