mptcp_get_available_schedulers() needs to iterate over the schedulers'
list only to read the names: it doesn't modify anything there.

In this case, it is enough to hold the RCU read lock, no need to combine
this with the associated spin lock.

Fixes: 73c900aa3660 ("mptcp: add net.mptcp.available_schedulers")
Cc: stable@vger.kernel.org
Suggested-by: Paolo Abeni <pabeni@redhat.com>
Reviewed-by: Geliang Tang <geliang@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
---
 net/mptcp/sched.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/net/mptcp/sched.c b/net/mptcp/sched.c
index 78ed508ebc1b8dd9f0e020cca1bdd86f24f0afeb..df7dbcfa3b71370cc4d7e4e4f16cc1e41a50dddf 100644
--- a/net/mptcp/sched.c
+++ b/net/mptcp/sched.c
@@ -60,7 +60,6 @@ void mptcp_get_available_schedulers(char *buf, size_t maxlen)
 	size_t offs = 0;
 
 	rcu_read_lock();
-	spin_lock(&mptcp_sched_list_lock);
 	list_for_each_entry_rcu(sched, &mptcp_sched_list, list) {
 		offs += snprintf(buf + offs, maxlen - offs,
 				 "%s%s",
@@ -69,7 +68,6 @@ void mptcp_get_available_schedulers(char *buf, size_t maxlen)
 		if (WARN_ON_ONCE(offs >= maxlen))
 			break;
 	}
-	spin_unlock(&mptcp_sched_list_lock);
 	rcu_read_unlock();
 }
 

-- 
2.45.2

On Mon, Oct 21, 2024 at 12:25:27PM +0200, Matthieu Baerts (NGI0) wrote:
> mptcp_get_available_schedulers() needs to iterate over the schedulers'
> list only to read the names: it doesn't modify anything there.
> 
> In this case, it is enough to hold the RCU read lock, no need to combine
> this with the associated spin lock.
> 
> Fixes: 73c900aa3660 ("mptcp: add net.mptcp.available_schedulers")
> Cc: stable@vger.kernel.org
> Suggested-by: Paolo Abeni <pabeni@redhat.com>
> Reviewed-by: Geliang Tang <geliang@kernel.org>
> Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>

I do wonder if it would be more appropriate to route this via net-next
(without a fixes tag) rather than via net. But either way this looks good
to me.

Reviewed-by: Simon Horman <horms@kernel.org>

...

Hi Simon,

Thank you for the reviews!

On 23/10/2024 14:21, Simon Horman wrote:
> On Mon, Oct 21, 2024 at 12:25:27PM +0200, Matthieu Baerts (NGI0) wrote:
>> mptcp_get_available_schedulers() needs to iterate over the schedulers'
>> list only to read the names: it doesn't modify anything there.
>>
>> In this case, it is enough to hold the RCU read lock, no need to combine
>> this with the associated spin lock.
>>
>> Fixes: 73c900aa3660 ("mptcp: add net.mptcp.available_schedulers")
>> Cc: stable@vger.kernel.org
>> Suggested-by: Paolo Abeni <pabeni@redhat.com>
>> Reviewed-by: Geliang Tang <geliang@kernel.org>
>> Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
> 
> I do wonder if it would be more appropriate to route this via net-next
> (without a fixes tag) rather than via net. But either way this looks good
> to me.
Good point. On one hand, I marked it as a fix, because when working on
the patch 1/3, we noticed these spin_(un)lock() were not supposed to be
there in the first place. On the other hand, even it's fixing a small
performance issue, it is not fixing a regression.

I think it is easier to route this via -net, but I'm fine if it is
applied in net-next.

Cheers,
Matt
-- 
Sponsored by the NGI0 Core fund.

On Wed, 23 Oct 2024 16:13:36 +0200 Matthieu Baerts wrote:
> On 23/10/2024 14:21, Simon Horman wrote:
> > On Mon, Oct 21, 2024 at 12:25:27PM +0200, Matthieu Baerts (NGI0) wrote:  
> >> mptcp_get_available_schedulers() needs to iterate over the schedulers'
> >> list only to read the names: it doesn't modify anything there.
> >>
> >> In this case, it is enough to hold the RCU read lock, no need to combine
> >> this with the associated spin lock.
> >>
> >> Fixes: 73c900aa3660 ("mptcp: add net.mptcp.available_schedulers")
> >> Cc: stable@vger.kernel.org
> >> Suggested-by: Paolo Abeni <pabeni@redhat.com>
> >> Reviewed-by: Geliang Tang <geliang@kernel.org>
> >> Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>  
> > 
> > I do wonder if it would be more appropriate to route this via net-next
> > (without a fixes tag) rather than via net. But either way this looks good
> > to me.  
> Good point. On one hand, I marked it as a fix, because when working on
> the patch 1/3, we noticed these spin_(un)lock() were not supposed to be
> there in the first place. On the other hand, even it's fixing a small
> performance issue, it is not fixing a regression.
> 
> I think it is easier to route this via -net, but I'm fine if it is
> applied in net-next.

I agree with Simon's initial response. Let's not blur the lines.
Please re-queue for net-next, I'll apply the rest.

BTW thanks a lot for proactively fixing the CONFIG_PROVE_RCU_LIST
splats!

On Wed, Oct 23, 2024 at 04:13:36PM +0200, Matthieu Baerts wrote:
> Hi Simon,
> 
> Thank you for the reviews!
> 
> On 23/10/2024 14:21, Simon Horman wrote:
> > On Mon, Oct 21, 2024 at 12:25:27PM +0200, Matthieu Baerts (NGI0) wrote:
> >> mptcp_get_available_schedulers() needs to iterate over the schedulers'
> >> list only to read the names: it doesn't modify anything there.
> >>
> >> In this case, it is enough to hold the RCU read lock, no need to combine
> >> this with the associated spin lock.
> >>
> >> Fixes: 73c900aa3660 ("mptcp: add net.mptcp.available_schedulers")
> >> Cc: stable@vger.kernel.org
> >> Suggested-by: Paolo Abeni <pabeni@redhat.com>
> >> Reviewed-by: Geliang Tang <geliang@kernel.org>
> >> Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
> > 
> > I do wonder if it would be more appropriate to route this via net-next
> > (without a fixes tag) rather than via net. But either way this looks good
> > to me.
> Good point. On one hand, I marked it as a fix, because when working on
> the patch 1/3, we noticed these spin_(un)lock() were not supposed to be
> there in the first place. On the other hand, even it's fixing a small
> performance issue, it is not fixing a regression.
> 
> I think it is easier to route this via -net, but I'm fine if it is
> applied in net-next.

Understood. FTR, I don't feel strongly about this either way.