Re: linux-next: Tree for Jun 21 [ BROKEN ipc/ipc-msg ]

[Sedat Dilek]

On Sat, Jun 22, 2013 at 12:07 AM, Davidlohr Bueso
<davidlohr.bueso@xxxxxx> wrote:
> On Fri, 2013-06-21 at 21:34 +0200, Sedat Dilek wrote:
>> On Fri, Jun 21, 2013 at 10:17 AM, Stephen Rothwell <sfr@xxxxxxxxxxxxxxxx> wrote:
>> > Hi all,
>> >
>> > Happy solstice!
>> >
>> > Changes since 20130620:
>> >
>> > Dropped tree: mailbox (really bad merge conflicts with the arm-soc tree)
>> >
>> > The net-next tree gained a conflict against the net tree.
>> >
>> > The leds tree still had its build failure, so I used the version from
>> > next-20130607.
>> >
>> > The arm-soc tree gained conflicts against the tip, net-next, mfd and
>> > mailbox trees.
>> >
>> > The staging tree still had its build failure for which I disabled some
>> > code.
>> >
>> > The akpm tree lost a few patches that turned up elsewhere and gained
>> > conflicts against the ftrace and arm-soc trees.
>> >
>> > ----------------------------------------------------------------------------
>> >
>>
>> [ CC IPC folks ]
>>
>> Building via 'make deb-pkg' with fakeroot fails here like this:
>>
>> make: *** [deb-pkg] Terminated
>> /usr/bin/fakeroot: line 181:  2386 Terminated
>> FAKEROOTKEY=$FAKEROOTKEY LD_LIBRARY_PATH="$PATHS" LD_PRELOAD="$LIB"
>> "$@"
>> semop(1): encountered an error: Identifier removed
>> semop(2): encountered an error: Invalid argument
>> semop(1): encountered an error: Identifier removed
>> semop(1): encountered an error: Identifier removed
>> semop(1): encountered an error: Invalid argument
>> semop(1): encountered an error: Invalid argument
>> semop(1): encountered an error: Invalid argument
>>
>
> Hmmm those really shouldn't be related to the message queue changes. Are
> you sure you got the right bisect?
>
> Manfred has a few ipc/sem.c patches in linux-next, starting at commit
> c50df1b4 (ipc/sem.c: cacheline align the semaphore structures), does
> reverting any of those instead of "ipc,msg: shorten critical region in
> msgrcv" help at all? Also, anything reported in dmesg?
>

First, I reverted all IPC patches from akpm-tree within -next.
Then, I isolated the culprit by git-bisecting.
As I checked my logs I did not see anything helpful.

>> The issue is present since next-20130606!
>>
>> LAST KNOWN GOOD: next-20130605
>> FIRST KNOWN BAD: next-20130606
>>
>> KNOWN GOOD: next-20130604
>> KNOWN BAD:  next-20130607 || next-20130619 || next-20130620 || next-20130621
>>
>> git-bisect says CULPRIT commit is...
>>
>>      "ipc,msg: shorten critical region in msgrcv"
>
> This I get. I went through the code again and it looks correct and
> functionally equivalent to the old msgrcv.
>

Hmm, I guess a rcu_read_unlock() is missing?

[ next-20130605 ]
...
		/* Lockless receive, part 3:
		 * Acquire the queue spinlock.
		 */
		ipc_lock_by_ptr(&msq->q_perm);
		rcu_read_unlock();
...
[ next-20130621 ]
...
		/* Lockless receive, part 3:
		 * Acquire the queue spinlock.
		 */
		ipc_lock_object(&msq->q_perm);
...

Whereas ipc_lock_by_ptr() is equivalent to:
rcu_read_lock();
ipc_lock_object();

>>
>> NOTE: msg_lock_(check_) routines have to be restored (one more revert needed)!
>
> This I don't get. Restoring msg_lock_[check] is already equivalent to
> reverting "ipc,msg: shorten critical region in msgrcv" and several other
> of the msq patches. What other patch needs reverted?
>

No, you have to revert both patches as the other removed
msg_lock_[check] afterwards.

> Anyway, I'll see if I can reproduce the issue, maybe I'm missing
> something.
>

Yupp, I try with adding rcu_read_unlock()... and report.

- Sedat -

> Thanks,
> Davidlohr
>
>>
>> Reverting both (below) commits makes fakeroot build via 'make dep-pkg" again.
>>
>> I have tested the revert-patches with next-20130606 and next-20130621
>> (see file-attachments).
>>
>> My build-script is attached!
>>
>> Can someone of the IPC folks look at that?
>> Thanks!
>>
>> - Sedat -
>>
>>
>> P.S.: Commit-IDs listed below.
>>
>> [ next-20130606 ]
>>
>> http://git.kernel.org/cgit/linux/kernel/git/next/linux-next.git/log/?id=next-20130606
>>
>> "ipc: remove unused functions"
>> http://git.kernel.org/cgit/linux/kernel/git/next/linux-next.git/commit/?id=8793fdfb0d0a6ed5916767e29a15d3eb56e04e79
>>
>> "ipc,msg: shorten critical region in msgrcv"
>> http://git.kernel.org/cgit/linux/kernel/git/next/linux-next.git/commit/?id=c0ff93322847a54f74a5450032c4df64c17fdaed
>>
>> [ next-20130621 ]
>>
>> http://git.kernel.org/cgit/linux/kernel/git/next/linux-next.git/log/?id=next-20130621
>>
>> "ipc: remove unused functions"
>> http://git.kernel.org/cgit/linux/kernel/git/next/linux-next.git/commit/?id=941ce57c81dcceadf55265616ee1e8bef18b0ad3
>>
>> "ipc,msg: shorten critical region in msgrcv"
>> http://git.kernel.org/cgit/linux/kernel/git/next/linux-next.git/commit/?id=62190df4081ee8504e3611d45edb40450cb408ac
>
>
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