From: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>
To: Matthew Wilcox <willy@infradead.org>
Cc: akpm@linux-foundation.org, Mike Kravetz <mike.kravetz@oracle.com>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH] mm/hugetlb: make hugetlb_lock irq safe
Date: Wed, 5 Sep 2018 18:56:19 +0530 [thread overview]
Message-ID: <d76771e6-1664-5d38-a5a0-e98f1120494c@linux.ibm.com> (raw)
In-Reply-To: <20180905130440.GA3729@bombadil.infradead.org>
On 09/05/2018 06:34 PM, Matthew Wilcox wrote:
> On Wed, Sep 05, 2018 at 04:53:41PM +0530, Aneesh Kumar K.V wrote:
>> inconsistent {SOFTIRQ-ON-W} -> {IN-SOFTIRQ-W} usage.
>
> How do you go from "can be taken in softirq context" problem report to
> "must disable hard interrupts" solution? Please explain why spin_lock_bh()
> is not a sufficient fix.
>
>> swapper/68/0 [HC0[0]:SC1[1]:HE1:SE0] takes:
>> 0000000052a030a7 (hugetlb_lock){+.?.}, at: free_huge_page+0x9c/0x340
>> {SOFTIRQ-ON-W} state was registered at:
>> lock_acquire+0xd4/0x230
>> _raw_spin_lock+0x44/0x70
>> set_max_huge_pages+0x4c/0x360
>> hugetlb_sysctl_handler_common+0x108/0x160
>> proc_sys_call_handler+0x134/0x190
>> __vfs_write+0x3c/0x1f0
>> vfs_write+0xd8/0x220
>
> Also, this only seems to trigger here. Is it possible we _already_
> have softirqs disabled through every other code path, and it's just this
> one sysctl handler that needs to disable softirqs? Rather than every
> lock access?
Are you asking whether I looked at moving that put_page to a worker
thread? I didn't. The reason I looked at current patch is to enable the
usage of put_page() from irq context. We do allow that for non hugetlb
pages. So was not sure adding that additional restriction for hugetlb
is really needed. Further the conversion to irqsave/irqrestore was
straightforward.
Now with respect to making sure we don't have irq already disabled in
those code paths, I did check that. But let me know if you find anything
I missed.
> I'm not seeing any analysis in this patch description, just a kneejerk
> "lockdep complained, must disable interrupts".
>
-aneesh
next prev parent reply other threads:[~2018-09-05 13:26 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-09-05 11:23 [RFC PATCH] mm/hugetlb: make hugetlb_lock irq safe Aneesh Kumar K.V
2018-09-05 13:04 ` Matthew Wilcox
2018-09-05 13:26 ` Aneesh Kumar K.V [this message]
2018-09-05 13:48 ` Matthew Wilcox
2018-09-05 19:58 ` Andrew Morton
2018-09-05 21:35 ` Mike Kravetz
2018-09-05 22:00 ` Andrew Morton
2018-09-05 23:07 ` Matthew Wilcox
2018-09-05 23:51 ` Mike Kravetz
2018-09-06 4:03 ` Aneesh Kumar K.V
2018-09-06 11:19 ` Michal Hocko
2018-09-06 3:58 ` Aneesh Kumar K.V
2018-09-06 3:54 ` Aneesh Kumar K.V
2018-09-06 4:00 ` Aneesh Kumar K.V
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