linux-kernel - [PATCH RT 0/2] rwsem-rt: Make rwsem rt closer to mainline

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Message-Id: <20140409024700.702797305@goodmis.org>
Date:	Tue, 08 Apr 2014 22:47:00 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	linux-kernel@...r.kernel.org,
	linux-rt-users <linux-rt-users@...r.kernel.org>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Carsten Emde <C.Emde@...dl.org>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	John Kacur <jkacur@...hat.com>,
	Paul Gortmaker <paul.gortmaker@...driver.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: [PATCH RT 0/2] rwsem-rt: Make rwsem rt closer to mainline

Looking at mainline's down_read() I noticed that reader locks of rwsems
are not made to nest. In fact, they should not. Although, it may seem
fine if a down_read() nests as multiple readers can have the lock,
rwsems are fair locks. That is, if a writer were to block on a rwsem
while readers have the lock, a new reader will also block. If a reader
were to try to take the lock again while a writer was waiting, it
would block, and cause a deadlock as it has the lock its trying
to grab and wont let it go as the writer is waiting.

I also found that the rt_mutex_init() is identical in the two places
it is defined in rtmutex.h.

Steven Rostedt (Red Hat) (2):
      rwsem-rt: Do not allow readers to nest
      rtmutex: Remove duplicate rt_mutex_init()

----
 include/linux/rtmutex.h  | 12 +++---------
 include/linux/rwsem_rt.h |  1 -
 kernel/rt.c              | 37 ++++++++-----------------------------
 3 files changed, 11 insertions(+), 39 deletions(-)
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