linux-kernel - Re: [PATCH -v2] seqlock, procfs: Match scoped_seqlock_read() critical section vs. RCU ordering in do_task_stat() to do_io

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Message-ID: <aS6vpLzte-9LqwYQ@redhat.com>
Date: Tue, 2 Dec 2025 10:21:40 +0100
From: Oleg Nesterov <oleg@...hat.com>
To: Ingo Molnar <mingo@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH -v2] seqlock, procfs: Match scoped_seqlock_read()
 critical section vs. RCU ordering in do_task_stat() to do_io_accounting()

On 12/02, Ingo Molnar wrote:
>
> * Oleg Nesterov <oleg@...hat.com> wrote:
>
> > On 12/02, Ingo Molnar wrote:
> > >
> > > RCU read-lock should not nest inside a read-seqlock
> > > irqsave ->stats_lock IRQs-off critical section,
> >
> > Hmm... I agree with this patch, but is it actually wrong?
> >
> > I thought that rcu_read_lock/unlock is safe under spin_lock_irq...
>
> Yeah, true - it's allowed and not a bug,

OK, thanks ;)

> merely
> discouraged inside irqs-off sections if it can be
> avoided, and it's an inconsistency versus
> do_io_accounting().

Yes, yes, agreed

> How about the -v2 phrasing below? I also removed the
> Fixes tags.

Acked-by: Oleg Nesterov <oleg@...hat.com>