Messages in this thread | | | Subject | Re: [PATCH] modules: fix livelock in add_unformed_module() | From | Prarit Bhargava <> | Date | Wed, 22 May 2019 13:08:56 -0400 |
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On 5/13/19 10:37 AM, Barret Rhoden wrote: > Hi - >
Hey Barret, my apologies for not getting back to you earlier. I got caught up in something that took me away from this issue.
> 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(). >
The more I look at this I think you're right. Let me do some additional testing with your patch + my original patch.
P.
> Barret
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