On 02/12/2014 03:03 AM, Andrew Morton wrote: > On Sun, 9 Feb 2014 14:56:15 +0400 Vladimir Davydov <vdavy...@parallels.com> > wrote: > >> Currently kobject_uevent has somewhat unpredictable semantics. The point >> is, since it may call a usermode helper and wait for it to execute >> (UMH_WAIT_EXEC), it is impossible to say for sure what lock dependencies >> it will introduce for the caller - strictly speaking it depends on what >> fs the binary is located on and the set of locks fork may take. There >> are quite a few kobject_uevent's users that do not take this into >> account and call it with various mutexes taken, e.g. rtnl_mutex, >> net_mutex, which might potentially lead to a deadlock. >> >> Since there is actually no reason to wait for the usermode helper to >> execute there, let's make kobject_uevent start the helper asynchronously >> with the aid of the UMH_NO_WAIT flag. >> >> Personally, I'm interested in this, because I really want kobject_uevent >> to be called under the slab_mutex in the slub implementation as it used >> to be some time ago, because it greatly simplifies synchronization and >> automatically fixes a kmemcg-related race. However, there was a deadlock >> detected on an attempt to call kobject_uevent under the slab_mutex (see >> https://lkml.org/lkml/2012/1/14/45), which was reported to be fixed by >> releasing the slab_mutex for kobject_uevent. Unfortunately, there was no >> information about who exactly blocked on the slab_mutex causing the >> usermode helper to stall, neither have I managed to find this out or >> reproduce the issue. >> >> BTW, this is not the first attempt to make kobject_uevent use >> UMH_NO_WAIT. Previous one was made by commit f520360d93c, but it was >> wrong (it passed arguments allocated on stack to async thread) so it was >> reverted (commit 05f54c13cd0c). It targeted on speeding up the boot >> process though. > The patches look good to me. One is kobject (Greg) and the other is > slub (Pekka), so I grabbed them ;) Reviews-and-acks, please? > > > > btw, when referring to commits, please use the form > > f520360d93c ("kobject: don't block for each kobject_uevent") > > because the same commit can have different hashes in different trees.
Oh, sorry about that. I will take this into account. Thank you. > > (Although I suspect the amount of convenience this provides others > doesn't match the amount of time I spend fixing changelogs!) > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
