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Date: Fri, 21 Jun 2013 16:11:45 -0700 From: Davidlohr Bueso <davidlohr.bueso@...com> To: sedat.dilek@...il.com Cc: linux-next@...r.kernel.org, linux-kernel@...r.kernel.org, Stephen Rothwell <sfr@...b.auug.org.au>, Andrew Morton <akpm@...ux-foundation.org>, linux-mm <linux-mm@...ck.org>, Andi Kleen <andi@...stfloor.org>, Rik van Riel <riel@...hat.com>, Manfred Spraul <manfred@...orfullife.com> Subject: Re: linux-next: Tree for Jun 21 [ BROKEN ipc/ipc-msg ] On Sat, 2013-06-22 at 00:54 +0200, Sedat Dilek wrote: > On Sat, Jun 22, 2013 at 12:07 AM, Davidlohr Bueso > <davidlohr.bueso@...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@...b.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(); Yeah, I noticed that, but it's not an error. In the older code we have rcu_read_lock (Lockless receive, part 1) [...] /* Lockless receive, part 3: * Acquire the queue spinlock. */ ipc_lock_by_ptr(&msq->q_perm); rcu_read_unlock(); Which translates to: rcu_read_lock (Lockless receive, part 1) [...] /* Lockless receive, part 3: * Acquire the queue spinlock. */ rcu_read_lock(); ipc_lock_object(); rcu_read_unlock(); And thus, after that last rcu_read_unlock we are left with rcu_read_lock() ipc_lock_object(); If you notice, that's exactly what is done in the new code, only much more readable: We do rcu_read_lock in the part 1, then in part 3, we acquire the spinlock via ipc_lock_object(&msq->q_perm) > >> > >> 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 > > > > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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