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Date: Wed, 11 Nov 2020 15:53:16 +0100
From: David Hildenbrand <david@...hat.com>
To: linux-kernel@...r.kernel.org
Cc: linux-mm@...ck.org, linuxppc-dev@...ts.ozlabs.org,
David Hildenbrand <david@...hat.com>, stable@...r.kernel.org,
Michael Ellerman <mpe@...erman.id.au>,
Benjamin Herrenschmidt <benh@...nel.crashing.org>,
Paul Mackerras <paulus@...ba.org>,
Rashmica Gupta <rashmica.g@...il.com>
Subject: [PATCH v2 2/8] powernv/memtrace: fix crashing the kernel when enabling concurrently
It's very easy to crash the kernel right now by simply trying to enable
memtrace concurrently, hammering on the "enable" interface
loop.sh:
#!/bin/bash
dmesg --console-off
while true; do
echo 0x40000000 > /sys/kernel/debug/powerpc/memtrace/enable
done
[root@...alhost ~]# loop.sh &
[root@...alhost ~]# loop.sh &
Resulting quickly in a kernel crash. Let's properly protect using a
mutex.
Fixes: 9d5171a8f248 ("powerpc/powernv: Enable removal of memory for in memory tracing")
Cc: stable@...r.kernel.org# v4.14+
Cc: Michael Ellerman <mpe@...erman.id.au>
Cc: Benjamin Herrenschmidt <benh@...nel.crashing.org>
Cc: Paul Mackerras <paulus@...ba.org>
Cc: Rashmica Gupta <rashmica.g@...il.com>
Signed-off-by: David Hildenbrand <david@...hat.com>
---
arch/powerpc/platforms/powernv/memtrace.c | 22 +++++++++++++++-------
1 file changed, 15 insertions(+), 7 deletions(-)
diff --git a/arch/powerpc/platforms/powernv/memtrace.c b/arch/powerpc/platforms/powernv/memtrace.c
index eea1f94482ff..0e42fe2d7b6a 100644
--- a/arch/powerpc/platforms/powernv/memtrace.c
+++ b/arch/powerpc/platforms/powernv/memtrace.c
@@ -30,6 +30,7 @@ struct memtrace_entry {
char name[16];
};
+static DEFINE_MUTEX(memtrace_mutex);
static u64 memtrace_size;
static struct memtrace_entry *memtrace_array;
@@ -279,6 +280,7 @@ static int memtrace_online(void)
static int memtrace_enable_set(void *data, u64 val)
{
+ int rc = -EAGAIN;
u64 bytes;
/*
@@ -291,25 +293,31 @@ static int memtrace_enable_set(void *data, u64 val)
return -EINVAL;
}
+ mutex_lock(&memtrace_mutex);
+
/* Re-add/online previously removed/offlined memory */
if (memtrace_size) {
if (memtrace_online())
- return -EAGAIN;
+ goto out_unlock;
}
- if (!val)
- return 0;
+ if (!val) {
+ rc = 0;
+ goto out_unlock;
+ }
/* Offline and remove memory */
if (memtrace_init_regions_runtime(val))
- return -EINVAL;
+ goto out_unlock;
if (memtrace_init_debugfs())
- return -EINVAL;
+ goto out_unlock;
memtrace_size = val;
-
- return 0;
+ rc = 0;
+out_unlock:
+ mutex_unlock(&memtrace_mutex);
+ return rc;
}
static int memtrace_enable_get(void *data, u64 *val)
--
2.26.2
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