From: Teemu Koponen <tkoponen@iki.fi>
To: Manfred Spraul <manfred@colorfullife.com>
Cc: linux-kernel@vger.kernel.org
Subject: Re: Opening of blocking FIFOs not reliable?
Date: Sun, 14 Aug 2005 03:40:34 -0700 [thread overview]
Message-ID: <5dd81f5a65eb47acb87fcf4953c88bf1@iki.fi> (raw)
In-Reply-To: <42FF19AC.6010502@colorfullife.com>
On Aug 14, 2005, at 3:15, Manfred Spraul wrote:
>> Opening a FIFO for WR_ONLY should release a previously blocked
>> RD_ONLY open. I suspect this is not guaranteed on a heavily loaded
>> Linux box.
>>
> Do you have a test case?
> IIRC we had that bug, and it was fixed by adding PIPE_WCOUNTER:
> PIPE_WRITERS counts the number of writers. This one is decreased
> during close(). PIPE_WCOUNTER counts how often a writer was seen. It's
> never decreased. Readers that wait for a writer wait until
> PIPE_WCOUNTER changes, they do not look at PIPE_WRITERS.
Ah, I missed the semantics of WCOUNTER. True, writer's open should
always release the reader' s open (as Alan pointed out).
I do have a test application, which experienced dead-locked readers'
opens before I artificially delayed writers' closes. The application
runs on PlanetLab, which uses VServer, though. I'll try to construct
next a minimal test case based on the application and reproduce the
behavior on a vanilla box...
Teemu
--
next prev parent reply other threads:[~2005-08-14 10:40 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-08-14 10:15 Manfred Spraul
2005-08-14 10:40 ` Teemu Koponen [this message]
-- strict thread matches above, loose matches on Subject: below --
2005-08-13 3:18 Teemu Koponen
2005-08-14 0:49 ` Alan Cox
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