From: Vivek Goyal <vgoyal@redhat.com>
To: Tejun Heo <tj@kernel.org>
Cc: axboe@kernel.dk, ctalbott@google.com, rni@google.com,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 04/13] block: make ioc get/put interface more conventional and fix race on alloction
Date: Wed, 26 Oct 2011 12:01:01 -0400 [thread overview]
Message-ID: <20111026160101.GB355@redhat.com> (raw)
In-Reply-To: <1319593719-19132-5-git-send-email-tj@kernel.org>
On Tue, Oct 25, 2011 at 06:48:30PM -0700, Tejun Heo wrote:
[..]
> @@ -1645,11 +1645,12 @@ static void blkiocg_attach_task(struct cgroup *cgrp, struct task_struct *tsk)
> {
> struct io_context *ioc;
>
> - task_lock(tsk);
> - ioc = tsk->io_context;
> - if (ioc)
> + /* we don't lose anything even if ioc allocation fails */
> + ioc = get_task_io_context(tsk, GFP_ATOMIC, NUMA_NO_NODE);
> + if (ioc) {
> ioc->cgroup_changed = 1;
> - task_unlock(tsk);
> + put_io_context(ioc);
> + }
We really don't need to create a new io context here if it is not present.
cgroup_changed is set so that reference to old sync cfqq is dropped and
a new one is assigned when new IO comes in. Given the fact that io context
is not even present for the task being attached, there is no way there
is associated cic and associated cfqq. So no need to set changed_cgroup=1.
Will it make sense to pass in additional parameter to get_task_io_context()
so that it takes a reference if ioc exists otherwise returns NULL. Or may
be another variant of get_task_io_context() function.
This is a minor issue though. Will just avoid creating iocontext memory
for task if one is not using CFQ in the system.
[..]
>
> +extern char __blk_test_mode[2];
> +#define blk_test_mode (__blk_test_mode[0])
> +
Looks like leftover of your testing code.
Thanks
Vivek
next prev parent reply other threads:[~2011-10-26 16:01 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-10-26 1:48 [PATCHSET block:for-3.2/core] rescue cfq from RCU death sprial :) Tejun Heo
2011-10-26 1:48 ` [PATCH 01/13] ida: make ida_simple_get/put() IRQ safe Tejun Heo
2011-10-26 4:42 ` Rusty Russell
2011-10-26 20:28 ` Tejun Heo
2011-10-26 1:48 ` [PATCH 02/13] block, cfq: move cfqd->cic_index to q->id Tejun Heo
2011-10-26 1:48 ` [PATCH 03/13] block: misc ioc cleanups Tejun Heo
2011-10-26 1:48 ` [PATCH 04/13] block: make ioc get/put interface more conventional and fix race on alloction Tejun Heo
2011-10-26 16:01 ` Vivek Goyal [this message]
2011-10-26 19:29 ` Tejun Heo
2011-10-26 21:30 ` [PATCH UPDATED " Tejun Heo
2011-10-26 1:48 ` [PATCH 05/13] block: misc updates to blk_get_queue() Tejun Heo
2011-10-26 1:48 ` [PATCH 06/13] block, cfq: misc updates to cfq_io_context Tejun Heo
2011-10-27 15:39 ` Vivek Goyal
2011-10-27 16:24 ` Tejun Heo
2011-10-26 1:48 ` [PATCH 07/13] block, cfq: move ioc ioprio/cgroup changed handling to cic Tejun Heo
2011-10-26 1:48 ` [PATCH 08/13] block, cfq: fix race condition in cic creation path and tighten locking Tejun Heo
2011-10-26 1:48 ` [PATCH 09/13] block, cfq: fix cic lookup locking Tejun Heo
2011-10-26 1:48 ` [PATCH 10/13] block, cfq: unlink cfq_io_context's immediately Tejun Heo
2011-10-26 19:48 ` Vivek Goyal
2011-10-26 19:55 ` Tejun Heo
2011-10-26 20:38 ` Vivek Goyal
2011-10-26 20:54 ` Tejun Heo
2011-10-26 21:31 ` [PATCH UPDATED " Tejun Heo
2011-10-27 14:31 ` Vivek Goyal
2011-10-27 16:17 ` Tejun Heo
2011-10-27 17:05 ` Vivek Goyal
2011-10-27 17:11 ` Tejun Heo
2011-10-26 1:48 ` [PATCH 11/13] block, cfq: remove delayed unlink Tejun Heo
2011-10-26 1:48 ` [PATCH 12/13] block, cfq: kill ioc_gone Tejun Heo
2011-10-26 1:48 ` [PATCH 13/13] block, cfq: kill cic->key Tejun Heo
2011-10-26 21:36 ` [PATCHSET block:for-3.2/core] rescue cfq from RCU death sprial :) Tejun Heo
2011-10-27 15:32 ` Vivek Goyal
2011-10-27 16:10 ` Tejun Heo
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