linux-toradex.git/ipc/sem.c, branch v3.17-rc4

ipc/sem.c: add a printk_once for semctl(GETNCNT/GETZCNT)

2014-06-06T23:08:15+00:00

The actual Linux implementation for semctl(GETNCNT) and semctl(GETZCNT)
always (since 0.99.10) reported a thread as sleeping on all semaphores
that are listed in the semop() call.

The documented behavior (both in the Linux man page and in the Single
Unix Specification) is that a task should be reported on exactly one
semaphore: The semaphore that caused the thread to got to sleep.

This patch adds a pr_info_once() that is triggered if a thread hits the
relevant case.

The code triggers slightly too often, otherwise it would be necessary to
replicate the old code.  As there are no known users of GETNCNT or
GETZCNT, this is done to prevent unnecessary bloat.

The task that triggered is reported with name (tsk->comm) and pid.

Signed-off-by: Manfred Spraul 
Acked-by: Davidlohr Bueso 
Cc: Michael Kerrisk 
Cc: Joe Perches 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

ipc/sem.c: make semctl(,,{GETNCNT,GETZCNT}) standard compliant

2014-06-06T23:08:15+00:00

SUSv4 clearly defines how semncnt and semzcnt must be calculated: A task
waits on exactly one semaphore: The semaphore from the first operation
in the sop array that cannot proceed.

The Linux implementation never followed the standard, it tried to count
all semaphores that might be the reason why a task sleeps.

This patch fixes that.

Note:
a) The implementation assumes that GETNCNT and GETZCNT are rare operations,
   therefore the code counts them only on demand.
   (If they wouldn't be rare, then the non-compliance would have
   been found earlier)

b) compared to the initial version of the patch, the BUG_ONs were removed
   and it was clarified that the new behavior conforms to SUS.

Back-compatibility concerns:

Manfred:

: - there is no application in Fedora that uses GETNCNT or GETZCNT.
:
: - application that use only single-sop semop() are also safe, the
:   difference only affects complex apps.
:
: - portable application are also safe, the new behavior is standard
:   compliant.
:
: But that's it.  The old behavior existed in Linux from 0.99.something
: until now.

Michael:

: * These operations seem to be very little used.  Grepping the public
:   source that is contained Fedora 20 source DVD, there appear to be no
:   uses.  Of course, this says nothing about uses in private /
:   non-mainstream FOSS code, but it seems likely that the same pattern
:   is followed there.
:
: * The existing behavior is hard enough to understand that I suspect
:   that no one understood it well enough to rely on it anyway
:   (especially as that behavior contradicted both man page and POSIX).
:
: So, there's a chance of breakage, but I estimate that it's minute.

Signed-off-by: Manfred Spraul 
Cc: Davidlohr Bueso 
Cc: Michael Kerrisk 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

ipc/sem.c: store which operation blocks in perform_atomic_semop()

2014-06-06T23:08:15+00:00

Preparation for the next patch:

In the slow-path of perform_atomic_semop(), store a pointer to the
operation that caused the operation to block.

Signed-off-by: Manfred Spraul 
Cc: Davidlohr Bueso 
Cc: Michael Kerrisk 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

ipc/sem.c: change perform_atomic_semop parameters

2014-06-06T23:08:15+00:00

Right now, perform_atomic_semop gets the content of sem_queue as
individual fields.  Changes that, instead pass a pointer to sem_queue.

This is a preparation for the next patch: it uses sem_queue to store the
reason why a task must sleep.

Signed-off-by: Manfred Spraul 
Cc: Davidlohr Bueso 
Cc: Michael Kerrisk 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

ipc/sem.c: remove code duplication

2014-06-06T23:08:15+00:00

count_semzcnt and count_semncnt are more of less identical.  The patch
creates a single function that either counts the number of tasks waiting
for zero or waiting due to a decrease operation.

Compared to the initial version, the BUG_ONs were removed.

Signed-off-by: Manfred Spraul 
Cc: Davidlohr Bueso 
Cc: Michael Kerrisk 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

ipc/sem.c: bugfix for semctl(,,GETZCNT)

2014-06-06T23:08:15+00:00

GETZCNT is supposed to return the number of threads that wait until a
semaphore value becomes 0.

The current implementation overlooks complex operations that contain
both wait-for-zero operation and operations that alter at least one
semaphore.

The patch fixes that.  It's intentionally copy&paste, this will be
cleaned up in the next patch.

Signed-off-by: Manfred Spraul 
Cc: Davidlohr Bueso 
Cc: Michael Kerrisk 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

ipc, kernel: clear whitespace

2014-06-06T23:08:14+00:00

trailing whitespace

Signed-off-by: Paul McQuade 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

ipc, kernel: use Linux headers

2014-06-06T23:08:14+00:00

Use #include  instead of 
Use #include  instead of 

Signed-off-by: Paul McQuade 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

ipc: constify ipc_ops

2014-06-06T23:08:14+00:00

There is no need to recreate the very same ipc_ops structure on every
kernel entry for msgget/semget/shmget.  Just declare it static and be
done with it.  While at it, constify it as we don't modify the structure
at runtime.

Found in the PaX patch, written by the PaX Team.

Signed-off-by: Mathias Krause 
Cc: PaX Team 
Cc: Davidlohr Bueso 
Cc: Manfred Spraul 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

ipc: remove braces for single statements

2014-01-28T05:02:39+00:00

Deal with checkpatch messages:
     WARNING: braces {} are not necessary for single statement blocks

Signed-off-by: Davidlohr Bueso 
Cc: Aswin Chandramouleeswaran 
Cc: Rik van Riel 
Acked-by: Manfred Spraul 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds