linux-kernel - [PATCH] x86/mm/ptdump: Fix soft lockup in page table walker.

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Date:   Fri, 10 Feb 2017 12:54:05 +0300
From:   Andrey Ryabinin <aryabinin@...tuozzo.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>, <x86@...nel.org>
CC:     Tobias Regnery <tobias.regnery@...il.com>,
        "Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Alexander Potapenko <glider@...gle.com>,
        <kasan-dev@...glegroups.com>, <linux-kernel@...r.kernel.org>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        <stable@...r.kernel.org>
Subject: [PATCH] x86/mm/ptdump: Fix soft lockup in page table walker.

CONFIG_KASAN=y needs a lot of virtual memory mapped for its shadow.
In that case ptdump_walk_pgd_level_core() takes a lot of time to
walk across all page tables and doing this without
a rescheduling causes soft lockups:

 NMI watchdog: BUG: soft lockup - CPU#3 stuck for 23s! [swapper/0:1]
 ...
 Call Trace:
  ptdump_walk_pgd_level_core+0x40c/0x550
  ptdump_walk_pgd_level_checkwx+0x17/0x20
  mark_rodata_ro+0x13b/0x150
  kernel_init+0x2f/0x120
  ret_from_fork+0x2c/0x40

I guess that this issue might arise even without KASAN on a huge
machines with several terabytes of RAM.

Stick cond_resched() in pgd loop to fix this.

Reported-by: Tobias Regnery <tobias.regnery@...il.com>
Signed-off-by: Andrey Ryabinin <aryabinin@...tuozzo.com>
Cc: <stable@...r.kernel.org>
---
 arch/x86/mm/dump_pagetables.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/x86/mm/dump_pagetables.c b/arch/x86/mm/dump_pagetables.c
index ea9c49a..8aa6bea 100644
--- a/arch/x86/mm/dump_pagetables.c
+++ b/arch/x86/mm/dump_pagetables.c
@@ -15,6 +15,7 @@
 #include <linux/debugfs.h>
 #include <linux/mm.h>
 #include <linux/init.h>
+#include <linux/sched.h>
 #include <linux/seq_file.h>

 #include <asm/pgtable.h>
@@ -406,6 +407,7 @@ static void ptdump_walk_pgd_level_core(struct seq_file *m, pgd_t *pgd,
 		} else
 			note_page(m, &st, __pgprot(0), 1);

+		cond_resched();
 		start++;
 	}

-- 
2.10.2