Re: [PATCH 5.15 00/23] 5.15.160-rc1 review

[Chuck Lever III]

> On May 29, 2024, at 4:59 PM, NeilBrown <neilb@xxxxxxx> wrote:
> 
> On Wed, 29 May 2024, Jon Hunter wrote:
>> On 29/05/2024 00:42, NeilBrown wrote:
>>> On Wed, 29 May 2024, NeilBrown wrote:
>>>> 
>>>> We probably just need to add "| TASK_FREEZABLE" in one or two places.
>>>> I'll post a patch for testing in a little while.
>>> 
>>> There is no TASK_FREEZABLE before v6.1.
>>> This isn't due to a missed backport. It is simply because of differences
>>> in the freezer in older kernels.
>>> 
>>> Please test this patch.
>>> 
>>> Thanks,
>>> NeilBrown
>>> 
>>> From 416bd6ae9a598e64931d34b76aa58f39b11841cd Mon Sep 17 00:00:00 2001
>>> From: NeilBrown <neilb@xxxxxxx>
>>> Date: Wed, 29 May 2024 09:38:22 +1000
>>> Subject: [PATCH] sunrpc: exclude from freezer when waiting for requests:
>>> 
>>> Prior to v6.1, the freezer will only wake a kernel thread from an
>>> uninterruptible sleep.  Since we changed svc_get_next_xprt() to use and
>>> IDLE sleep the freezer cannot wake it.  we need to tell the freezer to
>>> ignore it instead.
>>> 
>>> Fixes: 9b8a8e5e8129 ("nfsd: don't allow nfsd threads to be signalled.")
>>> Signed-off-by: NeilBrown <neilb@xxxxxxx>
>>> ---
>>>  net/sunrpc/svc_xprt.c | 2 ++
>>>  1 file changed, 2 insertions(+)
>>> 
>>> diff --git a/net/sunrpc/svc_xprt.c b/net/sunrpc/svc_xprt.c
>>> index b19592673eef..12e9293bd12b 100644
>>> --- a/net/sunrpc/svc_xprt.c
>>> +++ b/net/sunrpc/svc_xprt.c
>>> @@ -764,10 +764,12 @@ static struct svc_xprt *svc_get_next_xprt(struct svc_rqst *rqstp, long timeout)
>>>   clear_bit(RQ_BUSY, &rqstp->rq_flags);
>>>   smp_mb__after_atomic();
>>> 
>>> + freezer_do_not_count();
>>>   if (likely(rqst_should_sleep(rqstp)))
>>>   time_left = schedule_timeout(timeout);
>>>   else
>>>   __set_current_state(TASK_RUNNING);
>>> + freezer_count();
>>> 
>>>   try_to_freeze();
>>> 
>> 
>> 
>> Thanks. I gave this a try on top of v5.15.160-rc1, but I am still seeing
>> the following and the board hangs ...
>> 
>> Freezing of tasks failed after 20.004 seconds (1 tasks refusing to freeze, wq_busy=0):
>> 
>> So unfortunately this does not fix it :-(
> 
> Thanks for testing.
> I can only guess that you had an active NFSv4.1 mount and that the
> callback thread was causing problems.  Please try this.  I also changed
> to use freezable_schedule* which seems like a better interface to do the
> same thing.
> 
> If this doesn't fix it, we'll probably need to ask someone who remembers
> the old freezer code.
> 
> Thanks,
> NeilBrown
> 
> From 518f0c1150f988b3fe8e5e0d053a25c3aa6c7d44 Mon Sep 17 00:00:00 2001
> From: NeilBrown <neilb@xxxxxxx>
> Date: Wed, 29 May 2024 09:38:22 +1000
> Subject: [PATCH] sunrpc: exclude from freezer when waiting for requests:
> 
> Prior to v6.1, the freezer will only wake a kernel thread from an
> uninterruptible sleep.  Since we changed svc_get_next_xprt() to use and
> IDLE sleep the freezer cannot wake it.  we need to tell the freezer to
> ignore it instead.
> 
> To make this work with only upstream requests we would need
>  Commit f5d39b020809 ("freezer,sched: Rewrite core freezer logic")
> which allows non-interruptible sleeps to be woken by the freezer.
> 
> Fixes: 9b8a8e5e8129 ("nfsd: don't allow nfsd threads to be signalled.")
> Signed-off-by: NeilBrown <neilb@xxxxxxx>
> ---
> fs/nfs/callback.c     | 2 +-
> fs/nfsd/nfs4proc.c    | 3 ++-
> net/sunrpc/svc_xprt.c | 4 ++--
> 3 files changed, 5 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/nfs/callback.c b/fs/nfs/callback.c
> index 46a0a2d6962e..8fe143cad4a2 100644
> --- a/fs/nfs/callback.c
> +++ b/fs/nfs/callback.c
> @@ -124,7 +124,7 @@ nfs41_callback_svc(void *vrqstp)
> } else {
> spin_unlock_bh(&serv->sv_cb_lock);
> if (!kthread_should_stop())
> - schedule();
> + freezable_schedule();
> finish_wait(&serv->sv_cb_waitq, &wq);
> }
> }
> diff --git a/fs/nfsd/nfs4proc.c b/fs/nfsd/nfs4proc.c
> index 6779291efca9..e0ff2212866a 100644
> --- a/fs/nfsd/nfs4proc.c
> +++ b/fs/nfsd/nfs4proc.c
> @@ -38,6 +38,7 @@
> #include <linux/slab.h>
> #include <linux/kthread.h>
> #include <linux/namei.h>
> +#include <linux/freezer.h>
> 
> #include <linux/sunrpc/addr.h>
> #include <linux/nfs_ssc.h>
> @@ -1322,7 +1323,7 @@ static __be32 nfsd4_ssc_setup_dul(struct nfsd_net *nn, char *ipaddr,
> 
> /* allow 20secs for mount/unmount for now - revisit */
> if (kthread_should_stop() ||
> - (schedule_timeout(20*HZ) == 0)) {
> + (freezable_schedule_timeout(20*HZ) == 0)) {
> finish_wait(&nn->nfsd_ssc_waitq, &wait);
> kfree(work);
> return nfserr_eagain;
> diff --git a/net/sunrpc/svc_xprt.c b/net/sunrpc/svc_xprt.c
> index b19592673eef..3cf53e3140a5 100644
> --- a/net/sunrpc/svc_xprt.c
> +++ b/net/sunrpc/svc_xprt.c
> @@ -705,7 +705,7 @@ static int svc_alloc_arg(struct svc_rqst *rqstp)
> set_current_state(TASK_RUNNING);
> return -EINTR;
> }
> - schedule_timeout(msecs_to_jiffies(500));
> + freezable_schedule_timeout(msecs_to_jiffies(500));
> }
> rqstp->rq_page_end = &rqstp->rq_pages[pages];
> rqstp->rq_pages[pages] = NULL; /* this might be seen in nfsd_splice_actor() */
> @@ -765,7 +765,7 @@ static struct svc_xprt *svc_get_next_xprt(struct svc_rqst *rqstp, long timeout)
> smp_mb__after_atomic();
> 
> if (likely(rqst_should_sleep(rqstp)))
> - time_left = schedule_timeout(timeout);
> + time_left = freezable_schedule_timeout(timeout);
> else
> __set_current_state(TASK_RUNNING);
> 
> -- 
> 2.44.0

I will merge this into nfsd-5.10.

I can also run this past NFSD's upstream CI and send it along to
stable if you would like.


--
Chuck Lever