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From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: Mark Rutland <mark.rutland@arm.com>
Cc: linux-kernel@vger.kernel.org, ak@linux.intel.com,
	akpm@linux-foundation.org, bp@suse.de, catalin.marinas@arm.com,
	davem@davemloft.net, hch@lst.de, kan.liang@intel.com,
	mingo@kernel.org, peterz@infradead.org, riel@surriel.com,
	will@kernel.org
Subject: Re: [PATCH 8/9] x86/fpu: correctly check for kthreads
Date: Wed, 14 Aug 2019 16:55:37 +0200	[thread overview]
Message-ID: <20190814145537.fx73fwjvshpgdpue@linutronix.de> (raw)
In-Reply-To: <20190814133910.GC51963@lakrids.cambridge.arm.com>

On 2019-08-14 14:39:10 [+0100], Mark Rutland wrote:
 > I think this was missed in commit.
> > 	8d3289f2fa1e0 ("x86/fpu: Don't use current->mm to check for a kthread")
> 
> Yup, though if it's a bug it's been a bug since commit:
> 
>   0cecca9d03c964ab ("x86/fpu: Eager switch PKRU state")
> 
> ... which I guess the fixes tag would have to mention.
> 
> > 
> > A kthread with use_mm() would load here non-existing FPU state.
> > 
> > Acked-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> 
> Given the above, should I add the fixes tag (for 0cecca9d03c964ab)?

Buh. Either that or hch's commit (8d3289f2fa1e0 ("x86/fpu: Don't use
current->mm to check for a kthread").
That will trigger a stable backport (for 5.2) asking what to do about
is_kthread() so please leave a hint to use the PF_ flag like hch did.

Now that I think about it, even if we end up in kthread with use_mm()
then its FPU state is non-existent which means get_xsave_addr() returns
NULL. This is okay / expected but it triggers the WARN_ONCE().

> Thanks,
> Mark.

Sebastian

  reply	other threads:[~2019-08-14 14:55 UTC|newest]

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-08-14 10:41 [PATCH 0/9] kthread detection cleanup Mark Rutland
2019-08-14 10:41 ` [PATCH 1/9] sched/core: add is_kthread() helper Mark Rutland
2019-08-14 11:26   ` Geert Uytterhoeven
2019-08-14 11:32     ` Mark Rutland
2019-08-19  8:52       ` Ingo Molnar
2019-08-21 11:21         ` Peter Zijlstra
2019-08-14 10:41 ` [PATCH 2/9] sched: treewide: use is_kthread() Mark Rutland
2019-08-14 11:27   ` Geert Uytterhoeven
2019-08-14 12:39   ` Sebastian Andrzej Siewior
2019-08-14 13:35     ` Mark Rutland
2019-08-14 13:37   ` Valentin Schneider
2019-08-14 10:41 ` [PATCH 3/9] kmemleak: correctly check for kthreads Mark Rutland
2019-08-14 16:39   ` Catalin Marinas
2019-08-14 10:41 ` [PATCH 4/9] arm/perf: " Mark Rutland
2019-08-14 10:41 ` [PATCH 5/9] arm64: correctly check for ktrheads Mark Rutland
2019-08-14 16:40   ` Catalin Marinas
2019-08-14 10:41 ` [PATCH 6/9] sparc/perf: correctly check for kthreads Mark Rutland
2019-08-14 16:26   ` David Miller
2019-08-14 10:41 ` [PATCH 7/9] x86/lbr: " Mark Rutland
2019-08-14 10:41 ` [PATCH 8/9] x86/fpu: " Mark Rutland
2019-08-14 13:07   ` Sebastian Andrzej Siewior
2019-08-14 13:39     ` Mark Rutland
2019-08-14 14:55       ` Sebastian Andrzej Siewior [this message]
2019-08-14 10:41 ` [PATCH 9/9] samples/kretprobe: " Mark Rutland
2019-08-14 13:43 ` [PATCH 0/9] kthread detection cleanup Valentin Schneider

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