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Message-ID: <c29d47560629ca8866b0604abba60fda96ac0fbb.camel@kernel.org>
Date: Thu, 13 Feb 2025 07:34:12 -0500
From: Jeff Layton <jlayton@...nel.org>
To: Li Lingfeng <lilingfeng3@...wei.com>, 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
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.
--
Jeff Layton <jlayton@...nel.org>
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