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Message-ID: <859d17cf-6718-4557-8eed-9d79d46221cf@huawei.com>
Date: Thu, 13 Feb 2025 22:21:06 +0800
From: Li Lingfeng <lilingfeng3@...wei.com>
To: Jeff Layton <jlayton@...nel.org>, <chuck.lever@...cle.com>,
<neilb@...e.de>, <okorniev@...hat.com>, <Dai.Ngo@...cle.com>,
<tom@...pey.com>, <linux-nfs@...r.kernel.org>, <linux-kernel@...r.kernel.org>
CC: <yukuai1@...weicloud.com>, <houtao1@...wei.com>, <yi.zhang@...wei.com>,
<yangerkun@...wei.com>, <lilingfeng@...weicloud.com>
Subject: Re: [PATCH] nfsd: put dl_stid if fail to queue dl_recall
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@...wei.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.
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