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Koen Kooi
189ce92b4c
Signed-off-by: Koen Kooi <koen@dominion.thruhere.net> Signed-off-by: Denys Dmytriyenko <denys@ti.com>
65 lines
2.4 KiB
Diff
65 lines
2.4 KiB
Diff
From 8077f2d3611dd0c75c64f018c7e01dc2a4948a27 Mon Sep 17 00:00:00 2001
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From: Will Deacon <will.deacon@arm.com>
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Date: Fri, 20 Jan 2012 14:34:09 -0800
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Subject: [PATCH 123/129] proc: clear_refs: do not clear reserved pages
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commit 85e72aa5384b1a614563ad63257ded0e91d1a620 upstream.
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/proc/pid/clear_refs is used to clear the Referenced and YOUNG bits for
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pages and corresponding page table entries of the task with PID pid, which
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includes any special mappings inserted into the page tables in order to
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provide things like vDSOs and user helper functions.
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On ARM this causes a problem because the vectors page is mapped as a
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global mapping and since ec706dab ("ARM: add a vma entry for the user
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accessible vector page"), a VMA is also inserted into each task for this
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page to aid unwinding through signals and syscall restarts. Since the
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vectors page is required for handling faults, clearing the YOUNG bit (and
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subsequently writing a faulting pte) means that we lose the vectors page
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*globally* and cannot fault it back in. This results in a system deadlock
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on the next exception.
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To see this problem in action, just run:
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$ echo 1 > /proc/self/clear_refs
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on an ARM platform (as any user) and watch your system hang. I think this
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has been the case since 2.6.37
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This patch avoids clearing the aforementioned bits for reserved pages,
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therefore leaving the vectors page intact on ARM. Since reserved pages
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are not candidates for swap, this change should not have any impact on the
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usefulness of clear_refs.
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Signed-off-by: Will Deacon <will.deacon@arm.com>
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Reported-by: Moussa Ba <moussaba@micron.com>
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Acked-by: Hugh Dickins <hughd@google.com>
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Cc: David Rientjes <rientjes@google.com>
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Cc: Russell King <rmk@arm.linux.org.uk>
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Acked-by: Nicolas Pitre <nico@linaro.org>
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Cc: Matt Mackall <mpm@selenic.com>
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Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
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Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
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---
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fs/proc/task_mmu.c | 3 +++
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1 file changed, 3 insertions(+)
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diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
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index e418c5a..7dcd2a2 100644
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--- a/fs/proc/task_mmu.c
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+++ b/fs/proc/task_mmu.c
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@@ -518,6 +518,9 @@ static int clear_refs_pte_range(pmd_t *pmd, unsigned long addr,
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if (!page)
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continue;
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+ if (PageReserved(page))
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+ continue;
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+
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/* Clear accessed and referenced bits. */
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ptep_test_and_clear_young(vma, addr, pte);
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ClearPageReferenced(page);
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--
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1.7.9.5
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