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Date:   Tue, 17 Mar 2020 09:34:43 -0700
From:   Davidlohr Bueso <dave@stgolabs.net>
To:     Jason Baron <jbaron@akamai.com>
Cc:     akpm@linux-foundation.org, rpenyaev@suse.de,
        linux-kernel@vger.kernel.org, normalperson@yhbt.net,
        viro@zeniv.linux.org.uk
Subject: Re: [PATCH v2] fs/epoll: make nesting accounting safe for -rt kernel
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On Wed, 26 Feb 2020, Jason Baron wrote:

>Davidlohr Bueso pointed out that when CONFIG_DEBUG_LOCK_ALLOC is set
>ep_poll_safewake() can take several non-raw spinlocks after disabling
>interrupts. Since a spinlock can block in the -rt kernel, we can't take a
>spinlock after disabling interrupts. So let's re-work how we determine
>the nesting level such that it plays nicely with the -rt kernel.
>
>Let's introduce a 'nests' field in struct eventpoll that records the
>current nesting level during ep_poll_callback(). Then, if we nest again we
>can find the previous struct eventpoll that we were called from and
>increase our count by 1. The 'nests' field is protected by
>ep->poll_wait.lock.
>
>I've also moved the visited field to reduce the size of struct eventpoll
>from 184 bytes to 176 bytes on x86_64 for !CONFIG_DEBUG_LOCK_ALLOC,
>which is typical for a production config.
>
>Reported-by: Davidlohr Bueso <dbueso@suse.de>
>Signed-off-by: Jason Baron <jbaron@akamai.com>

Sorry for the tardy reply. This looks good to me:

Reviewed-by: Davidlohr Bueso <dbueso@suse.de>