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[Xen-ia64-devel] Re: [Xen-devel] [PATCH][PVFB][LINUX] Fix possible sleep

To: Markus Armbruster <armbru@xxxxxxxxxx>, Keir Fraser <keir@xxxxxxxxxxxxx>
Subject: [Xen-ia64-devel] Re: [Xen-devel] [PATCH][PVFB][LINUX] Fix possible sleep while holding spinlock
From: Atsushi SAKAI <sakaia@xxxxxxxxxxxxxx>
Date: Tue, 19 Dec 2006 11:52:09 +0900
Cc: xen-devel@xxxxxxxxxxxxxxxxxxx, xen-ia64-devel@xxxxxxxxxxxxxxxxxxx
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Hi, Markus

I tested on SMP DomU at xen-ia64-unstable 13083.
It seems works fine.

Atsushi SAKAI

>xenfb_update_screen() calls zap_page_range() while holding spinlock
>mm_lock.  Big no-no.
>Changeset 13018:c98ca86138a7422cdf9b15d87c95619b7277bb6a merely sweeps
>the bug under the carpet: it silences zap_page_range()'s cries for
>help by keeping interrupts enabled.  That doesn't fix the bug, and
>it's also wrong: if a critical region gets interrupted, and the
>interrupt printk()s, xenfb_refresh() gets executed and promptly
>This patch fixes the locking, but leaves open a race between
>xenfb_update_screen() and do_no_page().  See the source code for a
>detailed explanation of how it works, and where it fails.
>Signed-off-by: Markus Armbruster <armbru@xxxxxxxxxx>

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