Re: Hung task when calling clone() due to netfilter/slab
From: Eric W. Biederman <hidden>
Date: 2012-01-20 02:29:06
Christoph Lameter [off-list ref] writes:
On Thu, 19 Jan 2012, Eric W. Biederman wrote:quoted
Oh. I see. The problem is calling kobject_uevent (which happens to live in slabs sysfs_slab_add) with a lock held. And kobject_uevent makes a blocking call to userspace. No locks held seems to be a good policy on that one.Well we can just remove that call to kobject_uevent instead then. Does it do anything useful? Cannot remember why we put that in there.
Empirically it sounds like something is listening for it and doing cat /proc/slabinfo. Something like that would have to occur for their to be a deadlock that was observed. On the flip side removing from sysfs with locks held must be done carefully, and as a default I would recommend not to hold locks over removing things from sysfs. As removal blocks waiting for all of the callers into sysfs those sysfs attributes to complete. It looks like you are ok on the removal because none of the sysfs attributes appear to take the slub_lock, just /proc/slabinfo. But it does look like playing with fire. Eric -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>