linux-kernel - Re: [RFC][PATCH 3/3] staging: ion: Avoid using rt

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Mon, 16 Dec 2013 16:17:57 -0800
From:	Colin Cross <ccross@...roid.com>
To:	John Stultz <john.stultz@...aro.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Android Kernel Team <kernel-team@...roid.com>,
	Greg KH <gregkh@...uxfoundation.org>
Subject: Re: [RFC][PATCH 3/3] staging: ion: Avoid using rt_mutexes directly.

On Mon, Dec 16, 2013 at 1:32 PM, John Stultz <john.stultz@...aro.org> wrote:
> RT_MUTEXES can be configured out of the kernel, causing compile
> problems with ION.
>
> Since there is no documentation as to why directly using rt_mutexes
> is necessary (and very few drivers directly use rt_mutexes), simply
> convert the ion_heap lock to a normal mutex.

rt_mutexes were added with the deferred freeing feature.  Heaps need
to return zeroed memory to userspace, but zeroing the memory on every
allocation was causing performance issues.  We added a SCHED_IDLE
thread to zero memory in the background after freeing, but locking the
heap from the SCHED_IDLE thread might block a high priority allocation
thread for a long time.

The lock is only used to protect the heap's free_list and
free_list_size members, and is not held for any long or sleeping
operations.  Converting to a spinlock should prevent priority
inversion without using the rt_mutex.  I'd also rename it to free_lock
to so it doesn't get used as a general heap lock.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/