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

[Sedat Dilek <sedat.dilek@gmail.com>]

On Sat, Jun 22, 2013 at 12:54 AM, Sedat Dilek <sedat.dilek@gmail.com> wrote:
> On Sat, Jun 22, 2013 at 12:07 AM, Davidlohr Bueso
> <davidlohr.bueso@hp.com> 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@canb.auug.org.au> 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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