[PATCH] tapset: add a tapset function for reading epoch time in ARM

[David Smith]

On 06/12/2014 09:57 AM, Josh Stone wrote:
> The problem was with xtime_lock, now called timekeeper_seq.  If a probe
> occurs while that write lock is held, then calls getnstimeofday(), it
> would loop forever trying to get the read lock.  I don't see anything to
> make me think this has changed on modern kernels.

The following kernel commit converted xtime_lock/timekeeper_seq from a
seqlock into a seqcount. It now might be possible for systemtap to call
the kernel's gettimeofdayns()/do_gettimeofday() here without a
context/locking issue. This kernel commit entered the kernel in version
3.10.

====
commit 9a7a71b1d0968fc2bd602b7481cde1d4872e01ff
Author: Thomas Gleixner <tglx@linutronix.de>
Date:   Thu Feb 21 22:51:38 2013 +0000

    timekeeping: Split timekeeper_lock into lock and seqcount

    We want to shorten the seqcount write hold time. So split the seqlock
    into a lock and a seqcount.

    Open code the seqwrite_lock in the places which matter and drop the
    sequence counter update where it's pointless.

    Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
    [jstultz: Merge fixups from CLOCK_TAI collisions]
    Signed-off-by: John Stultz <john.stultz@linaro.org>
====

-- 
David Smith
dsmith@redhat.com
Red Hat
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