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From: Barret Rhoden <brho@google.com>
To: Prarit Bhargava <prarit@redhat.com>, Jessica Yu <jeyu@kernel.org>
Cc: linux-kernel@vger.kernel.org,
	Heiko Carstens <heiko.carstens@de.ibm.com>,
	David Arcari <darcari@redhat.com>
Subject: Re: [PATCH] modules: fix livelock in add_unformed_module()
Date: Mon, 13 May 2019 10:37:03 -0400	[thread overview]
Message-ID: <d968a588-c43b-cfe1-6358-6c5d99f916a3@google.com> (raw)
In-Reply-To: <dd48a3a4-9046-3917-55ba-d9eb391052b3@redhat.com>

Hi -

On 5/13/19 7:23 AM, Prarit Bhargava wrote:
[snip]
> A module is loaded once for each cpu.

Does one CPU succeed in loading the module, and the others fail with EEXIST?

> My follow-up patch changes from wait_event_interruptible() to
> wait_event_interruptible_timeout() so the CPUs are no longer sleeping and can
> make progress on other tasks, which changes the return values from
> wait_event_interruptible().
> 
> https://marc.info/?l=linux-kernel&m=155724085927589&w=2
> 
> I believe this also takes your concern into account?

That patch might work for me, but I think it papers over the bug where 
the check on old->state that you make before sleeping (was COMING || 
UNFORMED, now !LIVE) doesn't match the check to wake up in 
finished_loading().

The reason the issue might not show up in practice is that your patch 
basically polls, so the condition checks in finished_loading() are only 
a quicker exit.

If you squash my patch into yours, I think it will cover that case. 
Though if polling is the right answer here, it also raises the question 
of whether or not we even need finished_loading().

Barret

  reply	other threads:[~2019-05-13 14:37 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-04-30 22:22 [PATCH v3] kernel/module: Reschedule while waiting for modules to finish loading Prarit Bhargava
2019-05-01  7:49 ` Jessica Yu
2019-05-01 21:26 ` Prarit Bhargava
2019-05-02  9:48   ` Jessica Yu
2019-05-02 12:41     ` Prarit Bhargava
2019-05-02 17:46       ` Prarit Bhargava
2019-05-10 18:40         ` Barret Rhoden
2019-05-10 18:42           ` [PATCH] modules: fix livelock in add_unformed_module() Barret Rhoden
2019-05-13 11:23             ` Prarit Bhargava
2019-05-13 14:37               ` Barret Rhoden [this message]
2019-05-22 17:08                 ` Prarit Bhargava
2019-05-28 14:30                   ` Prarit Bhargava
2019-05-28 14:47                     ` Jessica Yu

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