linux-kernel - Re: [Resend PATCHv4 1/1] mm: fix incorrect vbq reference in purge_fragmented

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Date: Thu, 13 Jun 2024 17:11:06 +0800
From: hailong liu <hailong.liu@...o.com>
To: Baoquan He <bhe@...hat.com>
CC: Uladzislau Rezki <urezki@...il.com>, Zhaoyang Huang
	<huangzhaoyang@...il.com>, zhaoyang.huang <zhaoyang.huang@...soc.com>, Andrew
 Morton <akpm@...ux-foundation.org>, Christoph Hellwig <hch@...radead.org>,
	Lorenzo Stoakes <lstoakes@...il.com>, Thomas Gleixner <tglx@...utronix.de>,
	<linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>,
	<stable@...r.kernel.org>, <steve.kang@...soc.com>
Subject: Re: [Resend PATCHv4 1/1] mm: fix incorrect vbq reference in
 purge_fragmented_block

On Thu, 13. Jun 16:41, Baoquan He wrote:
> On 06/12/24 at 01:27pm, Uladzislau Rezki wrote:
> > On Wed, Jun 12, 2024 at 10:00:14AM +0800, Zhaoyang Huang wrote:
> > > On Wed, Jun 12, 2024 at 2:16 AM Uladzislau Rezki <urezki@...il.com> wrote:
> > > >
> > > > >
> > > > > Sorry to bother you again. Are there any other comments or new patch
> > > > > on this which block some test cases of ANDROID that only accept ACKed
> > > > > one on its tree.
> > > > >
> > > > I have just returned from vacation. Give me some time to review your
> > > > patch. Meanwhile, do you have a reproducer? So i would like to see how
> > > > i can trigger an issue that is in question.
> > > This bug arises from an system wide android test which has been
> > > reported by many vendors. Keep mount/unmount an erofs partition is
> > > supposed to be a simple reproducer. IMO, the logic defect is obvious
> > > enough to be found by code review.
> > >
> > Baoquan, any objection about this v4?
> >
> > Your proposal about inserting a new vmap-block based on it belongs
> > to, i.e. not per-this-cpu, should fix an issue. The problem is that
> > such way does __not__ pre-load a current CPU what is not good.
>
> With my understand, when we start handling to insert vb to vbq->xa and
> vbq->free, the vmap_area allocation has been done, it doesn't impact the
> CPU preloading when adding it into which CPU's vbq->free, does it?
>
> Not sure if I miss anything about the CPU preloading.
>
>

IIUC, if vb put by hashing funcation. and the following scenario may occur:

A kthread limit on CPU_x and continuously calls vm_map_ram()
The 1 call vm_map_ram(): no vb in cpu_x->free, so
CPU_0->vb
CPU_1
...
CPU_x

The 2 call vm_map_ram(): no vb in cpu_x->free, so
CPU_0->vb
CPU_1->vb
...
CPU_x

--
help you, help me,
Hailong.