From: Steven Rostedt <srostedt@redhat.com>
Date: Tue, 23 Dec 2008 16:32:25 +0000 (-0500)
Subject: ring-buffer: prevent false positive warning
X-Git-Tag: v2.6.29-rc1~586^2^4
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=98db8df777438e16ad0f44a0fba05ebbdb73db8d;p=pandora-kernel.git

ring-buffer: prevent false positive warning

Impact: eliminate false WARN_ON message

If an interrupt goes off after the setting of the local variable
tail_page and before incrementing the write index of that page,
the interrupt could push the commit forward to the next page.

Later a check is made to see if interrupts pushed the buffer around
the entire ring buffer by comparing the next page to the last commited
page. This can produce a false positive if the interrupt had pushed
the commit page forward as stated above.

Thanks to Jiaying Zhang for finding this race.

Reported-by: Jiaying Zhang <jiayingz@google.com>
Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Cc: <stable@kernel.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
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