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Torvald Riegel 4b35dc5dab futex.2: Terminology fixes 
Here is the result of a first pass over futex.2.  I tried to
do nothing that is too controversial.  I tried to apply the
terminology that at least Darren and I had in mind
consistently; but please check again.

The major changes are in how futexes are described in the
introductory parts of the page.  I hope it's easier to understand
now.  I've also tried to add some more precision to the the
description of the synchronization semantics (e.g., it makes a
difference whether we claim something is atomic (without further
qualification), or just atomic wrt.  other futex operations).
In some cases, that adds some verbosity to the text -- but I
believe that this is worth the clarity and consistency in using
terms, for example.

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
 2015-12-15 14:39:47 +01:00
Michael Kerrisk 77da5febea futex.2: tfix 
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
 2015-12-15 14:39:47 +01:00
Michael Kerrisk 305cc4153b futex.2: Add EXAMPLE program 
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
 2015-12-15 14:39:47 +01:00
Michael Kerrisk 02182e7c8c futex.2: srcfix: FIXME 
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
 2015-12-15 14:39:47 +01:00
Michael Kerrisk 1af427a43d futex.2: srcfix 
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
 2015-12-15 14:39:47 +01:00
Michael Kerrisk 47f5c4baf5 futex.2: srcfix: FIXME 
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
 2015-12-15 14:39:47 +01:00
Michael Kerrisk f529fd2013 futex Since Linux 2.6.22, EINTR can no longer occur on spurious wakeup 
As reported by Rich Felker:

    I see no code in the kernel whereby a "spurious wakeup",
    or anything other than interruption by a signal handler
    that's not SA_RESTART, can cause futex to fail with EINTR.
    In general, overloading of EINTR and/or spurious EINTRs
    from a syscall make it impossible to use that syscall for
    implementing any function where EINTR is a mandatory
    failure on interruption-by-signal, since there is no way
    for userspace to distinguish whether the EINTR occurred
    as a result of an interrupting signal or some other
    reason. The kernel folks have gone to great lengths to fix
    spurious EINTRs (see signal(7) for history), especially by
    non-interrupting signal handlers, including in futex, and
    allowing EINTR here would be contrary to that goal.

     It's my belief that the "or a spurious wakeup" text should
     simply be removed.

     The reason I'm raising this topic is its relevance to a
     thread on libc-alpha:

     [RFC] mutex destruction (#13690): problem description and workarounds

The bug and mailing list discussions to which Rich refers are:
     https://sourceware.org/bugzilla/show_bug.cgi?id=13690
     https://sourceware.org/ml/libc-alpha/2014-12/threads.html#0001

Torvald Riegel also reported the same issue, and Thomas Gleixner
noted that the "EINTR on spurious wakeup" behavior went away in
Linux 2.6.22. See the LKML thread, "futex() man page update help
request", Jan 2015:
http://thread.gmane.org/gmane.linux.kernel/1703405/focus=7734

Reported-by: Rich Felker <dalias@libc.org>
Reported-by: Torvald Riegel <triegel@redhat.com>
Reported-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Michael Kerrisk <mtknpages@gmail.com>
 2015-12-15 14:39:47 +01:00
Michael Kerrisk 9732dd8b3f futex.2: Various fixes after review from Davidlohr Bueso 
Reviewed-by: Davidlohr Bueso <dave@stgolabs.net>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
 2015-12-15 14:39:47 +01:00
Michael Kerrisk 2abcba676a futex.2: Remove FUTEX_REQUEUE EINVAL error case 
Thomas Gleixner confirmed my reading that this case does
not apply.

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
 2015-12-15 14:39:47 +01:00
Michael Kerrisk 9e2b90ee42 futex.2: Add an attmpt at a defintion of PI-aware futexes 
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
 2015-12-15 14:39:47 +01:00
Michael Kerrisk 7bd3ffbc52 futex.2: srcfix 
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
 2015-12-15 14:39:47 +01:00
Michael Kerrisk d9d5be6bea futex.2: tfix 
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
 2015-12-15 14:39:46 +01:00
Michael Kerrisk 809ca3ae64 futex.2: Note that the kernel only "knows" about a futex in the contended case 
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
 2015-12-15 14:39:46 +01:00
Michael Kerrisk a663ca5a12 futex.2: Add some subsection headings 
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
 2015-12-15 14:39:46 +01:00
Michael Kerrisk e219551457 futex.2: srcfix 
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
 2015-12-15 14:39:46 +01:00
Michael Kerrisk ed44c7c071 futex.2: Rewrite text on intended users of futexes 
Eliminate some redundant text.

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
 2015-12-15 14:39:46 +01:00
Michael Kerrisk abb571e8b7 futex.2: Add text on pairing of FUTEX_WAIT_REQUEUE_PI + FUTEX_CMP_REQUEUE_PI 
Reported-by: Darren Hart <dvhart@linux.intel.com>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
 2015-12-15 14:39:46 +01:00
Michael Kerrisk f1d2171d38 futex.2: srcfix 
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
 2015-12-15 14:39:46 +01:00
Michael Kerrisk bdc5957afa futex.2: Process/thread rewordings 
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
 2015-12-15 14:39:46 +01:00
Michael Kerrisk a59564304a futex.2: srcfix 
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
 2015-12-15 14:39:46 +01:00
Michael Kerrisk 6700de2462 futex.2: tfix 
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
 2015-12-15 14:39:46 +01:00
Michael Kerrisk 7d20efd7b0 futex.2: Add overview of priority inheritance 
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
 2015-12-15 14:39:46 +01:00
Michael Kerrisk b565548bfa futex.2: Add brief description of the priority inversion problem 
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
 2015-12-15 14:39:46 +01:00
Michael Kerrisk dd003bef7a futex.2: srcfix: FIXME 
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
 2015-12-15 14:39:46 +01:00
Michael Kerrisk 8fe019c733 futex.2: SEE ALSO: add Documentation/robust-futex-ABI.txt 
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
 2015-12-15 14:39:46 +01:00
Michael Kerrisk 4cf9289452 futex.2: tfix 
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
 2015-12-15 14:39:46 +01:00
Michael Kerrisk baf0f1f470 futex.2: Note that syscall() must be employed 
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
 2015-12-15 14:39:46 +01:00
Michael Kerrisk 4c2222812b futex.2: SEEL ALSO: add author details + other minor tweaks 
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
 2015-12-15 14:39:46 +01:00
Michael Kerrisk 939ca89f38 futex.2: wfix 
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
 2015-12-15 14:39:46 +01:00
Michael Kerrisk d4ba43283d futex.2: wfix 
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
 2015-12-15 14:39:46 +01:00
Michael Kerrisk a282e5b050 futex.2: wfix 
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
 2015-12-15 14:39:46 +01:00
Michael Kerrisk 30ebf7b4a1 futex.2: srcfix: FIXME 
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
 2015-12-15 14:39:46 +01:00
Michael Kerrisk 7f315ae3e5 futex.2: ffix 
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
 2015-12-15 14:39:46 +01:00
Michael Kerrisk 43d16602be futex.2: srcfix: FIXME 
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
 2015-12-15 14:39:46 +01:00
Michael Kerrisk 64191e8f09 futex.2: srcfix: FIXME 
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
 2015-12-15 14:39:46 +01:00
Michael Kerrisk f2bf5121d5 futex.2: srcfix 
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
 2015-12-15 14:39:46 +01:00
Michael Kerrisk 53ba4030d1 futex.2: grfix 
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
 2015-12-15 14:39:46 +01:00
Michael Kerrisk 4e566b1ebd futex.2: wfix 
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
 2015-12-15 14:39:45 +01:00
Michael Kerrisk e45f973525 futex.2: Clarify that FUTEX_PRIVATE_FLAG relates to *thread* synchronization 
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
 2015-12-15 14:39:45 +01:00
Michael Kerrisk f19904c01c futex.2: wfix: mention "virtual" when talking about memory addreses 
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
 2015-12-15 14:39:45 +01:00
Michael Kerrisk 70b06b9033 futex.2: srcfix 
Various minor fixes to source

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
 2015-12-15 14:39:45 +01:00
Michael Kerrisk a59fca7505 futex.2: wfix 
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
 2015-12-15 14:39:45 +01:00
Michael Kerrisk 21b060bae6 futex.2: wfix 
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
 2015-12-15 14:39:45 +01:00
Michael Kerrisk 5d67b190a1 futex.2: srcfix: FIXME 
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
 2015-12-15 14:39:45 +01:00
Michael Kerrisk f0c0d61cd8 futex.2: ERRORS: add EINVAL case for FUTEX_CMP_REQUEUE_PI 
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
 2015-12-15 14:39:45 +01:00
Michael Kerrisk 99c0ac69d9 futex.2: srcfix: FIXME 
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
 2015-12-15 14:39:45 +01:00
Michael Kerrisk 9786b3ca15 futex.2: ERRORS: Add EINVAL case for FUTEX_CMP_REQUEUE_PI 
Reported-by: Darren Hart <dvhart@linux.intel.com>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
 2015-12-15 14:39:45 +01:00
Michael Kerrisk 75299c8d17 futex.2: Fix EINVAL description for FUTEX_CMP_REQUEUE_PI 
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
 2015-12-15 14:39:45 +01:00
Michael Kerrisk 6fbeb8f4a0 futex.2: Minor improvement to FUTEX_CMP_REQUEUE_PI text 
Reported-by: Darren Hart <dvhart@linux.intel.com>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
 2015-12-15 14:39:45 +01:00
Michael Kerrisk 55a8bca383 futex.2: srcfix: remove obsolete FIXME 
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
 2015-12-15 14:39:45 +01:00