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From: Yan Zhao <[email protected]>
To: Christoph Hellwig <[email protected]>
Cc: Jens Axboe <[email protected]>, Felipe Balbi <[email protected]>,
	"Michael S. Tsirkin" <[email protected]>,
	Jason Wang <[email protected]>,
	[email protected],
	Felix Kuehling <[email protected]>,
	[email protected], [email protected],
	[email protected], [email protected],
	[email protected], Zhenyu Wang <[email protected]>,
	[email protected], [email protected],
	Alex Deucher <[email protected]>,
	Andrew Morton <[email protected]>,
	[email protected],
	Linus Torvalds <[email protected]>,
	Zhi Wang <[email protected]>,
	Al Viro <[email protected]>
Subject: Re: [PATCH 2/6] i915/gvt/kvm: a NULL ->mm does not mean a thread is a kthread
Date: Tue, 14 Apr 2020 03:03:44 -0400	[thread overview]
Message-ID: <20200414070344.GF10586@joy-OptiPlex-7040> (raw)
In-Reply-To: <[email protected]>

On Tue, Apr 14, 2020 at 09:00:13AM +0200, Christoph Hellwig wrote:
> On Mon, Apr 13, 2020 at 08:04:10PM -0400, Yan Zhao wrote:
> > > I can't think of another way for a kernel thread to have a mm indeed.
> > for example, before calling to vfio_dma_rw(), a kernel thread has already
> > called use_mm(), then its current->mm is not null, and it has flag
> > PF_KTHREAD.
> > in this case, we just want to allow the copy_to_user() directly if
> > current->mm == mm, rather than call another use_mm() again.
> > 
> > do you think it makes sense?
> 
> I mean no other way than using use_mm.  That being said nesting
> potentional use_mm callers sounds like a rather bad idea, and we
> should avoid that.
yes, agree.
I was explaining why we just use "current->mm == NULL"
(not "current->flag & PF_KTHREAD") as a criteria to call use_mm()
in vfio_dma_rw(), which you might ask us when you take that part into your
series. :)

  reply	other threads:[~2020-04-14  7:13 UTC|newest]

Thread overview: 21+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-04-04  9:40 improve use_mm / unuse_mm Christoph Hellwig
2020-04-04  9:40 ` [PATCH 1/6] amdgpu: a NULL ->mm does not mean a thread is a kthread Christoph Hellwig
2020-04-06 16:07   ` Felix Kuehling
2020-04-04  9:40 ` [PATCH 2/6] i915/gvt/kvm: " Christoph Hellwig
2020-04-04 10:05   ` Sergei Shtylyov
2020-04-07  3:08   ` Yan Zhao
2020-04-13 13:27     ` Christoph Hellwig
2020-04-14  0:04       ` Yan Zhao
2020-04-14  7:00         ` Christoph Hellwig
2020-04-14  7:03           ` Yan Zhao [this message]
2020-04-04  9:40 ` [PATCH 3/6] i915/gvt: remove unused xen bits Christoph Hellwig
2020-04-08  1:44   ` Zhenyu Wang
2020-04-13 13:08     ` Christoph Hellwig
2020-04-14  3:04       ` Zhenyu Wang
2020-04-04  9:40 ` [PATCH 4/6] kernel: move use_mm/unuse_mm to kthread.c Christoph Hellwig
2020-04-06 16:09   ` Felix Kuehling
2020-04-04  9:41 ` [PATCH 5/6] kernel: better document the use_mm/unuse_mm API contract Christoph Hellwig
2020-04-04 13:07   ` [Intel-gfx] " Pavel Begunkov
2020-04-06 16:10   ` Felix Kuehling
2020-04-04  9:41 ` [PATCH 6/6] kernel: set USER_DS in kthread_use_mm Christoph Hellwig
2020-04-06 21:49   ` Michael S. Tsirkin

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