Re: [PATCH v5 06/13] lockdep: Implement crossrelease feature

From	Peter Zijlstra <peterz@infradead.org>
Newsgroups	linux.kernel
Subject	Re: [PATCH v5 06/13] lockdep: Implement crossrelease feature
Date	2017-02-28 20:50 +0100
Message-ID	<tfVWy-rZ-9@gated-at.bofh.it> (permalink)
References	<t0YjD-4z4-5@gated-at.bofh.it> <t0Ytl-4D1-41@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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On Wed, Jan 18, 2017 at 10:17:32PM +0900, Byungchul Park wrote:
> +	/*
> +	 * Each work of workqueue might run in a different context,
> +	 * thanks to concurrency support of workqueue. So we have to
> +	 * distinguish each work to avoid false positive.
> +	 *
> +	 * TODO: We can also add dependencies between two acquisitions
> +	 * of different work_id, if they don't cause a sleep so make
> +	 * the worker stalled.
> +	 */
> +	unsigned int		work_id;

> +/*
> + * Crossrelease needs to distinguish each work of workqueues.
> + * Caller is supposed to be a worker.
> + */
> +void crossrelease_work_start(void)
> +{
> +	if (current->xhlocks)
> +		current->work_id++;
> +}

So what you're trying to do with that 'work_id' thing is basically wipe
the entire history when we're at the bottom of a context.

Which is a useful operation, but should arguably also be done on the
return to userspace path. Any historical lock from before the current
syscall is irrelevant.

(And we should not be returning to userspace with locks held anyway --
lockdep already has a check for that).

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Re: [PATCH v5 06/13] lockdep: Implement crossrelease feature Peter Zijlstra <peterz@infradead.org> - 2017-02-28 20:50 +0100
  Re: [PATCH v5 06/13] lockdep: Implement crossrelease feature Byungchul Park <byungchul.park@lge.com> - 2017-03-01 08:30 +0100
    Re: [PATCH v5 06/13] lockdep: Implement crossrelease feature Peter Zijlstra <peterz@infradead.org> - 2017-03-01 11:50 +0100
      Re: [PATCH v5 06/13] lockdep: Implement crossrelease feature Byungchul Park <byungchul.park@lge.com> - 2017-03-01 13:30 +0100
  Re: [PATCH v5 06/13] lockdep: Implement crossrelease feature Matthew Wilcox <willy@infradead.org> - 2017-03-02 05:50 +0100
    RE: [PATCH v5 06/13] lockdep: Implement crossrelease feature "byungchul.park" <byungchul.park@lge.com> - 2017-03-02 07:20 +0100
      Re: [PATCH v5 06/13] lockdep: Implement crossrelease feature Matthew Wilcox <willy@infradead.org> - 2017-03-02 15:50 +0100
        Re: [PATCH v5 06/13] lockdep: Implement crossrelease feature Byungchul Park <byungchul.park@lge.com> - 2017-03-03 01:00 +0100
          Re: [PATCH v5 06/13] lockdep: Implement crossrelease feature Byungchul Park <byungchul.park@lge.com> - 2017-03-05 09:10 +0100

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