linux-kernel - SMP read() stopping at memory page boundaries

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Message-Id: <1182351171.3768.65.camel@hurina>
Date:	Wed, 20 Jun 2007 17:52:51 +0300
From:	Timo Sirainen <tss@....fi>
To:	linux-kernel@...r.kernel.org
Subject: SMP read() stopping at memory page boundaries

Tested with various 2.6.x i386/x86-64 SMP kernels and CPUs, for example
2.6.21.3/x86-64.

Process 1:

 - lock file
 - write(4096 + 16 bytes)
 - unlock file

Process 2:

 - lock file
 - read(8192 bytes)
 - unlock file

Sometimes read() returns only 4096 bytes. I'm locking the file, so I
don't think this should ever happen, right?

Attached a test program. Takes from a few seconds to half a minute with
my computer to print "page size cut".

View attachment "concurrency2.c" of type "text/x-csrc" (1556 bytes)

Download attachment "signature.asc" of type "application/pgp-signature" (190 bytes)