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powerpc/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@localhost ~]# loop.sh &
[root@localhost ~]# loop.sh &

Resulting quickly in a kernel crash. Let's properly protect using a
mutex.

Fixes: 9d5171a8f2 ("powerpc/powernv: Enable removal of memory for in memory tracing")
Cc: stable@vger.kernel.org# v4.14+
Signed-off-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Oscar Salvador <osalvador@suse.de>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20201111145322.15793-3-david@redhat.com
zero-sugar-mainline-defconfig
David Hildenbrand 2020-11-11 15:53:16 +01:00 committed by Michael Ellerman
parent c74cf7a3d5
commit d6718941a2
1 changed files with 15 additions and 7 deletions
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22
arch/powerpc/platforms/powernv/memtrace.c
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@ -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)