Re: [PATCH] driver core: fix shutdown races with probe/remove(v2)
From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Date: 2012-06-15 22:03:49
Also in:
lkml
On Mon, Jun 11, 2012 at 01:13:20PM +0800, Ming Lei wrote:
Firstly, .shutdown callback may touch a uninitialized hardware if dev->driver is set and .probe is not completed. Secondly, device_shutdown() may dereference a null pointer to cause oops when dev->driver is cleared after it is checked in device_shutdown(). So just try to hold device lock and its parent lock(if it has) to fix the races. Cc: Alan Stern <stern@rowland.harvard.edu> Cc: stable@vger.kernel.org
Why stable? Are there known systems that crash right now without this change? I don't think we ever heard back from the original poster about this issue as to what exactly was going wrong.
quoted hunk ↗ jump to hunk
Signed-off-by: Ming Lei <redacted> --- v2: - take Alan's suggestion to use device_trylock to avoid hanging during shutdown by buggy device or driver - hold parent reference counter drivers/base/core.c | 32 ++++++++++++++++++++++++++++++++ 1 file changed, 32 insertions(+)diff --git a/drivers/base/core.c b/drivers/base/core.c index 346be8b..f2fc989 100644 --- a/drivers/base/core.c +++ b/drivers/base/core.c@@ -1796,6 +1796,16 @@ out: } EXPORT_SYMBOL_GPL(device_move); +static int __try_lock(struct device *dev) +{ + int i = 0; + + while (!device_trylock(dev) && i++ < 100) + msleep(10); + + return i < 100; +}
That's a totally arbritary time, why does this work and other times do not? And what is this returning, if the lock was grabbed successfully? What's with the __ naming? I really don't like this at all.
quoted hunk ↗ jump to hunk
+ /** * device_shutdown - call ->shutdown() on each device to shutdown. */@@ -1810,8 +1820,11 @@ void device_shutdown(void) * devices offline, even as the system is shutting down. */ while (!list_empty(&devices_kset->list)) { + int nonlocked; + dev = list_entry(devices_kset->list.prev, struct device, kobj.entry); + get_device(dev->parent);
Why grab the parent reference?
quoted hunk ↗ jump to hunk
get_device(dev); /* * Make sure the device is off the kset list, in the@@ -1820,6 +1833,18 @@ void device_shutdown(void) list_del_init(&dev->kobj.entry); spin_unlock(&devices_kset->list_lock); + /* hold lock to avoid race with .probe/.release */ + if (dev->parent && !__try_lock(dev->parent)) + nonlocked = 2; + else if (!__try_lock(dev)) + nonlocked = 1; + else + nonlocked = 0;
Ick ick ick. Why can't we just grab the lock to try to only call these callbacks one at a time? What is causing the big problem here that I am missing?
+ + if (nonlocked) + dev_err(dev, "can't hold %slock for shutdown\n", + nonlocked == 1 ? "" : "parent ");
What can anyone do with this message? I sure wouldn't know what to do with it, do you? If so, what? greg k-h