linux-kernel - Re: [patch] IA64: suppress return value of down_trylock() in salinfo_work_to

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Date:	Sun, 03 Aug 2008 12:08:08 +1000
From:	Keith Owens <kaos@....com.au>
To:	Matthew Wilcox <matthew@....cx>
cc:	Simon Horman <horms@...ge.net.au>, linux-ia64@...r.kernel.org,
	linux-kernel@...r.kernel.org, Tony Luck <tony.luck@...el.com>
Subject: Re: [patch] IA64: suppress return value of down_trylock() in salinfo_work_to_do() 

Matthew Wilcox (on Sat, 2 Aug 2008 19:32:00 -0600) wrote:
>On Sun, Aug 03, 2008 at 10:06:58AM +1000, Simon Horman wrote:
>> salinfo_work_to_do() intentionally ignores the return value of
>> down_trylock() and calls up() regardless of if the lock
>> was taken or not.
>> 
>> This patch suppresses the warning generated by ignoring
>> this return value - down_trylock() is annotated with __must_check.
>
>I can't say that I think this is a good idea.  Has anyone looked at what
>it would take to actually track this?  For example, could we ever have
>the situation where:
>
>task A acquires sem
>
>task B tries to acquire the sem, fails
>task B releases the sem that it didn't acquire
>
>task A releases the sem, falls down, goes boom?

Cannot happen.  See the comment above the function:

  This routine must be called with data_saved_lock held, to make the down/up
  operation atomic

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