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watchdog: refuse to unload softdog module when its timer is running

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the softdog has static variables which are accessed if its timer is
still running after the driver is unloaded. and lead to crash:

   $modprobe softdog
   $echo 1 >/dev/watchdog
   $modprobe -r softdog

   CPU 20 Unable to handle kernel paging request at virtual address
   Oops[#1]:
   CPU: 20 PID: 0 Comm: swapper/20 Not tainted 4.1.13-WR8.0.0.0_standard
   ...
   Modules linked in: [last unloaded: softdog]
    ....
   Call Trace:
   [<ffffffff801e142c>] cascade+0x34/0xb0
   [<ffffffff801e1964>] run_timer_softirq+0x30c/0x368
   [<ffffffff80181044>] __do_softirq+0x1ec/0x418
   [<ffffffff801815d0>] irq_exit+0x90/0x98
   [<ffffffff8010749c>] plat_irq_dispatch+0xa4/0x140
   [<ffffffff80152740>] ret_from_irq+0x0/0x4
   [<ffffffff801529e0>] __r4k_wait+0x20/0x40
   [<ffffffff801c2278>] cpu_startup_entry+0x2a0/0x368
   [<ffffffff8015fa64>] start_secondary+0x444/0x4d8

add the module ref when timer is running to avoid to unload the softdog
module

Signed-off-by: Li RongQing <roy.qing.li@gmail.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>
This commit is contained in:
Li RongQing 2015-12-17 21:30:02 +08:00 committed by Wim Van Sebroeck
parent 8d2fa17151
commit 5889f06bd3
1 changed files with 6 additions and 2 deletions
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8
drivers/watchdog/softdog.c
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@ -86,6 +86,7 @@ static struct timer_list watchdog_ticktock =
static void watchdog_fire(unsigned long data)
{
module_put(THIS_MODULE);
if (soft_noboot)
pr_crit("Triggered - Reboot ignored\n");
else if (soft_panic) {
@ -104,13 +105,16 @@ static void watchdog_fire(unsigned long data)
static int softdog_ping(struct watchdog_device *w)
{
mod_timer(&watchdog_ticktock, jiffies+(w->timeout*HZ));
if (!mod_timer(&watchdog_ticktock, jiffies+(w->timeout*HZ)))
__module_get(THIS_MODULE);
return 0;
}
static int softdog_stop(struct watchdog_device *w)
{
del_timer(&watchdog_ticktock);
if (del_timer(&watchdog_ticktock))
module_put(THIS_MODULE);
return 0;
}