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From: "Srivatsa S. Bhat" <srivatsa.bhat@linux.vnet.ibm.com>
To: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: peterz@infradead.org, fweisbec@gmail.com,
	linux-kernel@vger.kernel.org, Paul Mackerras <paulus@samba.org>,
	walken@google.com, mingo@kernel.org, linux-arch@vger.kernel.org,
	vincent.guittot@linaro.org, xiaoguangrong@linux.vnet.ibm.com,
	wangyun@linux.vnet.ibm.com, paulmck@linux.vnet.ibm.com,
	nikunj@linux.vnet.ibm.com, linux-pm@vger.kernel.org,
	rusty@rustcorp.com.au, rostedt@goodmis.org,
	Ian Munsie <imunsie@au1.ibm.com>,
	namhyung@kernel.org, tglx@linutronix.de, laijs@cn.fujitsu.com,
	zhong@linux.vnet.ibm.com, netdev@vger.kernel.org,
	oleg@redhat.com, sbw@mit.edu, tj@kernel.org,
	akpm@linux-foundation.org, linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH 40/45] powerpc, irq: Use GFP_ATOMIC allocations in atomic context
Date: Wed, 26 Jun 2013 00:50:01 +0530	[thread overview]
Message-ID: <51C9ED61.1060306@linux.vnet.ibm.com> (raw)
In-Reply-To: <1372130007.3944.185.camel@pasglop>

On 06/25/2013 08:43 AM, Benjamin Herrenschmidt wrote:
> On Tue, 2013-06-25 at 12:58 +1000, Michael Ellerman wrote:
>> On Tue, Jun 25, 2013 at 12:13:04PM +1000, Benjamin Herrenschmidt wrote:
>>> On Tue, 2013-06-25 at 12:08 +1000, Michael Ellerman wrote:
>>>> We're not checking for allocation failure, which we should be.
>>>>
>>>> But this code is only used on powermac and 85xx, so it should probably
>>>> just be a TODO to fix this up to handle the failure.
>>>
>>> And what can we do if they fail ?
>>
>> Fail up the chain and not unplug the CPU presumably.
> 
> BTW. Isn't Srivatsa series removing the need to stop_machine() for
> unplug ? 

Yes.

That should mean we should be able to use GFP_KERNEL no ?

No, because whatever code was being executed in stop_machine() context
would still be executed with interrupts disabled. So allocations that
can sleep would continue to be forbidden in this path.

In the CPU unplug sequence, the CPU_DYING notifications (and the surrounding
code) is guaranteed to be run:
a. _on_ the CPU going offline
b. with interrupts disabled on that CPU.

My patchset will retain these guarantees even after removing stop_machine().
And these are required for the correct execution of the code in this path,
since they rely on these semantics.

So I guess I'll retain the patch as it is. Thank you!

Regards,
Srivatsa S. Bhat

  reply	other threads:[~2013-06-25 19:23 UTC|newest]

Thread overview: 67+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2013-06-23 13:37 [PATCH 00/45] CPU hotplug: stop_machine()-free CPU hotplug, part 1 Srivatsa S. Bhat
2013-06-23 13:38 ` [PATCH 01/45] CPU hotplug: Provide APIs to prevent CPU offline from atomic context Srivatsa S. Bhat
2013-06-24 22:49   ` Steven Rostedt
2013-06-23 13:38 ` [PATCH 02/45] CPU hotplug: Clarify the usage of different synchronization APIs Srivatsa S. Bhat
2013-06-23 13:38 ` [PATCH 03/45] Documentation, CPU hotplug: Recommend usage of get/put_online_cpus_atomic() Srivatsa S. Bhat
2013-06-23 13:38 ` [PATCH 04/45] CPU hotplug: Add infrastructure to check lacking hotplug synchronization Srivatsa S. Bhat
2013-06-24 23:26   ` Steven Rostedt
2013-06-25 18:49     ` Srivatsa S. Bhat
2013-06-23 13:39 ` [PATCH 05/45] CPU hotplug: Protect set_cpu_online() to avoid false-positives Srivatsa S. Bhat
2013-06-23 13:39 ` [PATCH 06/45] CPU hotplug: Sprinkle debugging checks to catch locking bugs Srivatsa S. Bhat
2013-06-23 13:39 ` [PATCH 07/45] CPU hotplug: Expose the new debug config option Srivatsa S. Bhat
2013-06-23 15:08   ` Sergei Shtylyov
2013-06-23 18:58     ` Srivatsa S. Bhat
2013-06-23 13:39 ` [PATCH 08/45] CPU hotplug: Convert preprocessor macros to static inline functions Srivatsa S. Bhat
2013-06-23 13:40 ` [PATCH 09/45] smp: Use get/put_online_cpus_atomic() to prevent CPU offline Srivatsa S. Bhat
2013-06-23 13:40 ` [PATCH 10/45] sched/core: " Srivatsa S. Bhat
2013-06-23 13:40 ` [PATCH 11/45] migration: Use raw_spin_lock/unlock since interrupts are already disabled Srivatsa S. Bhat
2013-06-23 13:40 ` [PATCH 12/45] sched/fair: Use get/put_online_cpus_atomic() to prevent CPU offline Srivatsa S. Bhat
2013-06-23 13:40 ` [PATCH 13/45] timer: " Srivatsa S. Bhat
2013-06-23 13:41 ` [PATCH 14/45] sched/rt: " Srivatsa S. Bhat
2013-06-23 13:41 ` [PATCH 15/45] rcu: " Srivatsa S. Bhat
2013-06-23 13:41 ` [PATCH 16/45] tick-broadcast: " Srivatsa S. Bhat
2013-06-23 13:41 ` [PATCH 17/45] time/clocksource: " Srivatsa S. Bhat
2013-06-23 13:42 ` [PATCH 18/45] softirq: " Srivatsa S. Bhat
2013-06-23 13:42 ` [PATCH 19/45] irq: " Srivatsa S. Bhat
2013-06-23 13:42 ` [PATCH 20/45] net: " Srivatsa S. Bhat
2013-06-23 13:42 ` [PATCH 21/45] block: " Srivatsa S. Bhat
2013-06-23 13:42 ` [PATCH 22/45] percpu_counter: " Srivatsa S. Bhat
2013-06-24 17:55   ` Tejun Heo
2013-06-24 18:06     ` Tejun Heo
2013-06-24 18:09       ` Srivatsa S. Bhat
2013-06-23 13:43 ` [PATCH 23/45] infiniband: ehca: " Srivatsa S. Bhat
2013-06-23 13:43 ` [PATCH 24/45] [SCSI] fcoe: " Srivatsa S. Bhat
2013-06-23 13:43 ` [PATCH 25/45] staging/octeon: " Srivatsa S. Bhat
2013-06-23 18:17   ` Greg Kroah-Hartman
2013-06-23 18:55     ` Srivatsa S. Bhat
2013-06-23 19:17       ` Joe Perches
2013-06-24 17:25         ` Srivatsa S. Bhat
2013-06-24 18:17       ` David Daney
2013-06-23 13:43 ` [PATCH 26/45] x86: " Srivatsa S. Bhat
2013-06-23 13:43 ` [PATCH 27/45] perf/x86: " Srivatsa S. Bhat
2013-06-23 13:44 ` [PATCH 28/45] KVM: " Srivatsa S. Bhat
2013-06-23 13:44 ` [PATCH 29/45] kvm/vmx: " Srivatsa S. Bhat
2013-06-23 13:44 ` [PATCH 30/45] x86/xen: " Srivatsa S. Bhat
2013-06-23 13:45 ` [PATCH 31/45] alpha/smp: " Srivatsa S. Bhat
2013-06-23 17:50   ` Matt Turner
2013-06-23 18:56     ` Srivatsa S. Bhat
2013-06-23 13:45 ` [PATCH 32/45] blackfin/smp: " Srivatsa S. Bhat
2013-06-23 13:45 ` [PATCH 33/45] cris/smp: " Srivatsa S. Bhat
2013-06-24  6:41   ` Jesper Nilsson
2013-06-23 13:45 ` [PATCH 34/45] hexagon/smp: " Srivatsa S. Bhat
2013-06-23 13:45 ` [PATCH 35/45] ia64: irq, perfmon: " Srivatsa S. Bhat
2013-06-23 13:46 ` [PATCH 36/45] ia64: smp, tlb: " Srivatsa S. Bhat
2013-06-23 13:46 ` [PATCH 37/45] m32r: " Srivatsa S. Bhat
2013-06-23 13:46 ` [PATCH 38/45] MIPS: " Srivatsa S. Bhat
2013-06-23 13:46 ` [PATCH 39/45] mn10300: " Srivatsa S. Bhat
2013-06-23 13:47 ` [PATCH 40/45] powerpc, irq: Use GFP_ATOMIC allocations in atomic context Srivatsa S. Bhat
2013-06-25  2:08   ` Michael Ellerman
2013-06-25  2:13     ` Benjamin Herrenschmidt
2013-06-25  2:58       ` Michael Ellerman
2013-06-25  3:13         ` Benjamin Herrenschmidt
2013-06-25 19:20           ` Srivatsa S. Bhat [this message]
2013-06-23 13:47 ` [PATCH 41/45] powerpc: Use get/put_online_cpus_atomic() to prevent CPU offline Srivatsa S. Bhat
2013-06-23 13:47 ` [PATCH 42/45] powerpc: Use get/put_online_cpus_atomic() to avoid false-positive warning Srivatsa S. Bhat
2013-06-23 13:47 ` [PATCH 43/45] sh: Use get/put_online_cpus_atomic() to prevent CPU offline Srivatsa S. Bhat
2013-06-23 13:48 ` [PATCH 44/45] sparc: " Srivatsa S. Bhat
2013-06-23 13:48 ` [PATCH 45/45] tile: " Srivatsa S. Bhat

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