From: Oleg Nesterov <oleg@redhat.com>
To: Ingo Molnar <mingo@kernel.org>
Cc: Dave Hansen <dave.hansen@intel.com>, Borislav Petkov <bp@suse.de>,
Andy Lutomirski <luto@amacapital.net>,
Linus Torvalds <torvalds@linux-foundation.org>,
Pekka Riikonen <priikone@iki.fi>, Rik van Riel <riel@redhat.com>,
Suresh Siddha <sbsiddha@gmail.com>,
LKML <linux-kernel@vger.kernel.org>,
"Yu, Fenghua" <fenghua.yu@intel.com>,
Quentin Casasnovas <quentin.casasnovas@oracle.com>
Subject: Re: [PATCH 1/1] x86/fpu: math_state_restore() should not blindly disable irqs
Date: Thu, 5 Mar 2015 22:25:32 +0100 [thread overview]
Message-ID: <20150305212532.GA16890@redhat.com> (raw)
In-Reply-To: <20150305201101.GA21571@gmail.com>
On 03/05, Ingo Molnar wrote:
>
> * Oleg Nesterov <oleg@redhat.com> wrote:
>
> > --- a/arch/x86/kernel/traps.c
> > +++ b/arch/x86/kernel/traps.c
> > @@ -774,7 +774,10 @@ void math_state_restore(void)
> > struct task_struct *tsk = current;
> >
> > if (!tsk_used_math(tsk)) {
> > - local_irq_enable();
> > + bool disabled = irqs_disabled();
> > +
> > + if (disabled)
> > + local_irq_enable();
> > /*
> > * does a slab alloc which can sleep
> > */
> > @@ -785,7 +788,9 @@ void math_state_restore(void)
> > do_group_exit(SIGKILL);
> > return;
> > }
> > - local_irq_disable();
> > +
> > + if (disabled)
> > + local_irq_disable();
> > }
>
> Yuck!
>
> Is there a fundamental reason why we cannot simply enable irqs and
> leave them enabled? Math state restore is not atomic and cannot really
> be atomic.
You know, I didn't even try to verify ;) but see below.
Most probably we can simply enable irqs, yes. But what about older kernels,
how can we check?
And let me repeat, I strongly believe that this !tsk_used_math() case in
math_state_restore() must die. And unlazy_fpu() in init_fpu(). And both
__restore_xstate_sig() and flush_thread() should not use math_state_restore()
at all. At least in its current form.
But this is obviously not -stable material.
That said, I'll try to look into git history tomorrow. The patch above
looks "obviously safe", but perhaps I am paranoid too much...
Oleg.
next prev parent reply other threads:[~2015-03-05 21:27 UTC|newest]
Thread overview: 126+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-03-04 18:30 Oops with tip/x86/fpu Dave Hansen
2015-03-04 19:06 ` Oleg Nesterov
2015-03-04 19:12 ` Dave Hansen
2015-03-04 20:06 ` Borislav Petkov
2015-03-05 15:14 ` Oleg Nesterov
[not found] ` <20150305182203.GA4203@redhat.com>
2015-03-05 18:34 ` Dave Hansen
2015-03-05 18:46 ` Oleg Nesterov
2015-03-05 18:41 ` Dave Hansen
2015-03-26 22:37 ` Yu, Fenghua
2015-03-26 22:43 ` Dave Hansen
2015-03-26 22:48 ` Yu, Fenghua
2015-03-27 7:30 ` Quentin Casasnovas
2015-03-27 19:06 ` Oleg Nesterov
2015-03-05 8:38 ` Quentin Casasnovas
2015-03-05 15:13 ` Oleg Nesterov
2015-03-05 18:42 ` Borislav Petkov
2015-03-05 22:16 ` Dave Hansen
2015-03-05 19:51 ` [PATCH 0/1] x86/fpu: math_state_restore() should not blindly disable irqs Oleg Nesterov
2015-03-05 19:51 ` [PATCH 1/1] " Oleg Nesterov
2015-03-05 20:11 ` Ingo Molnar
2015-03-05 21:25 ` Oleg Nesterov [this message]
2015-03-06 7:58 ` Ingo Molnar
2015-03-06 13:26 ` Oleg Nesterov
2015-03-06 13:39 ` Oleg Nesterov
2015-03-06 13:46 ` Ingo Molnar
2015-03-06 14:01 ` Oleg Nesterov
2015-03-06 14:17 ` Oleg Nesterov
2015-03-06 15:00 ` David Vrabel
2015-03-06 15:36 ` Oleg Nesterov
2015-03-06 16:15 ` David Vrabel
2015-03-06 16:31 ` Oleg Nesterov
2015-03-06 17:33 ` Linus Torvalds
2015-03-06 18:15 ` Oleg Nesterov
2015-03-06 19:23 ` Andy Lutomirski
2015-03-06 22:00 ` Linus Torvalds
2015-03-06 22:28 ` Andy Lutomirski
2015-03-07 10:36 ` Ingo Molnar
2015-03-07 20:11 ` Linus Torvalds
2015-03-08 8:55 ` Ingo Molnar
2015-03-08 11:38 ` Ingo Molnar
2015-03-08 13:59 ` Andy Lutomirski
2015-03-08 14:38 ` Andy Lutomirski
2015-03-07 10:32 ` Ingo Molnar
2015-03-07 15:38 ` [PATCH 0/1] x86/fpu: x86/fpu: avoid math_state_restore() without used_math() in __restore_xstate_sig() Oleg Nesterov
2015-03-07 15:38 ` [PATCH 1/1] " Oleg Nesterov
2015-03-09 14:07 ` Borislav Petkov
2015-03-09 14:34 ` Oleg Nesterov
2015-03-09 15:18 ` Borislav Petkov
2015-03-09 16:24 ` Oleg Nesterov
2015-03-09 16:53 ` Borislav Petkov
2015-03-09 17:05 ` Oleg Nesterov
2015-03-09 17:23 ` Borislav Petkov
2015-03-16 12:07 ` [tip:x86/urgent] x86/fpu: Avoid " tip-bot for Oleg Nesterov
2015-03-05 20:35 ` [PATCH 0/1] x86/fpu: math_state_restore() should not blindly disable irqs Oleg Nesterov
2015-03-09 17:10 ` [PATCH] x86/fpu: drop_fpu() should not assume that tsk == current Oleg Nesterov
2015-03-09 17:36 ` Rik van Riel
2015-03-09 17:48 ` Borislav Petkov
2015-03-09 18:06 ` Oleg Nesterov
2015-03-09 18:10 ` Borislav Petkov
2015-03-16 12:07 ` [tip:x86/urgent] x86/fpu: Drop_fpu() should not assume that tsk equals current tip-bot for Oleg Nesterov
2015-03-11 17:33 ` [PATCH 0/4] x86/fpu: avoid math_state_restore() on kthread exec Oleg Nesterov
2015-03-11 17:34 ` [PATCH 1/4] x86/fpu: document user_fpu_begin() Oleg Nesterov
2015-03-13 9:47 ` Borislav Petkov
2015-03-13 14:34 ` Oleg Nesterov
2015-03-23 12:20 ` [tip:x86/fpu] x86/fpu: Document user_fpu_begin() tip-bot for Oleg Nesterov
2015-03-11 17:34 ` [PATCH 2/4] x86/fpu: introduce restore_init_xstate() Oleg Nesterov
2015-03-13 10:34 ` Borislav Petkov
2015-03-13 14:39 ` Oleg Nesterov
2015-03-13 15:20 ` Borislav Petkov
2015-03-16 19:05 ` Rik van Riel
2015-03-23 12:20 ` [tip:x86/fpu] x86/fpu: Introduce restore_init_xstate() tip-bot for Oleg Nesterov
2015-03-11 17:34 ` [PATCH 3/4] x86/fpu: use restore_init_xstate() instead of math_state_restore() on kthread exec Oleg Nesterov
2015-03-13 10:48 ` Borislav Petkov
2015-03-13 14:45 ` Oleg Nesterov
2015-03-13 15:51 ` Borislav Petkov
2015-03-23 12:21 ` [tip:x86/fpu] x86/fpu: Use " tip-bot for Oleg Nesterov
2015-03-11 17:35 ` [PATCH 4/4] x86/fpu: don't abuse drop_init_fpu() in flush_thread() Oleg Nesterov
2015-03-13 10:52 ` Borislav Petkov
2015-03-13 14:55 ` Oleg Nesterov
2015-03-13 16:19 ` Borislav Petkov
2015-03-13 16:26 ` Oleg Nesterov
2015-03-13 19:27 ` Borislav Petkov
2015-03-14 14:48 ` Oleg Nesterov
2015-03-15 17:36 ` Borislav Petkov
2015-03-15 18:16 ` Oleg Nesterov
2015-03-15 18:50 ` Borislav Petkov
2015-03-15 20:04 ` Oleg Nesterov
2015-03-15 20:38 ` Borislav Petkov
2015-03-16 9:35 ` Borislav Petkov
2015-03-16 10:28 ` Ingo Molnar
2015-03-16 14:39 ` Oleg Nesterov
2015-03-16 15:26 ` Borislav Petkov
2015-03-16 15:34 ` Andy Lutomirski
2015-03-16 15:35 ` Borislav Petkov
2015-03-13 17:30 ` [PATCH v2 " Oleg Nesterov
2015-03-14 10:55 ` Borislav Petkov
2015-03-14 10:57 ` [PATCH] x86/fpu: Fold __drop_fpu() into its sole user Borislav Petkov
2015-03-14 15:15 ` Oleg Nesterov
2015-03-16 10:27 ` Ingo Molnar
2015-03-23 12:21 ` [tip:x86/fpu] x86/fpu: Don't abuse drop_init_fpu() in flush_thread() tip-bot for Oleg Nesterov
2015-03-13 18:26 ` [PATCH 0/1] x86/cpu: don't allocate fpu->state for swapper/0 Oleg Nesterov
2015-03-13 18:27 ` [PATCH 1/1] " Oleg Nesterov
2015-03-16 10:18 ` Borislav Petkov
2015-03-23 12:22 ` [tip:x86/fpu] x86/fpu: Don't " tip-bot for Oleg Nesterov
2015-03-14 11:16 ` [PATCH 0/1] x86/cpu: don't " Borislav Petkov
2015-03-14 15:13 ` [PATCH 0/1] x86/cpu: kill eager_fpu_init_bp() Oleg Nesterov
2015-03-14 15:13 ` [PATCH 1/1] " Oleg Nesterov
2015-03-16 12:44 ` Borislav Petkov
2015-03-23 12:22 ` [tip:x86/fpu] x86/fpu: Kill eager_fpu_init_bp() tip-bot for Oleg Nesterov
2015-03-15 16:49 ` [PATCH RFC 0/2] x86/fpu: avoid "xstate_fault" in xsave_user/xrestore_user Oleg Nesterov
2015-03-15 16:50 ` [PATCH RFC 1/2] x86: introduce __user_insn() and __check_insn() Oleg Nesterov
2015-03-15 16:50 ` [PATCH RFC 2/2] x86/fpu: change xsave_user() and xrestore_user() to use __user_insn() Oleg Nesterov
2015-03-16 22:43 ` Quentin Casasnovas
2015-03-17 9:35 ` Borislav Petkov
2015-03-16 14:36 ` [PATCH RFC 0/2] x86/fpu: avoid "xstate_fault" in xsave_user/xrestore_user Borislav Petkov
2015-03-16 14:57 ` Oleg Nesterov
2015-03-16 17:58 ` Borislav Petkov
2015-03-16 22:37 ` Quentin Casasnovas
2015-03-17 9:47 ` Borislav Petkov
2015-03-17 10:00 ` Quentin Casasnovas
2015-03-17 11:20 ` Borislav Petkov
2015-03-17 11:36 ` Quentin Casasnovas
2015-03-17 12:07 ` Borislav Petkov
2015-03-18 9:06 ` Quentin Casasnovas
2015-03-18 9:53 ` Borislav Petkov
2015-03-17 10:07 ` Quentin Casasnovas
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20150305212532.GA16890@redhat.com \
--to=oleg@redhat.com \
--cc=bp@suse.de \
--cc=dave.hansen@intel.com \
--cc=fenghua.yu@intel.com \
--cc=linux-kernel@vger.kernel.org \
--cc=luto@amacapital.net \
--cc=mingo@kernel.org \
--cc=priikone@iki.fi \
--cc=quentin.casasnovas@oracle.com \
--cc=riel@redhat.com \
--cc=sbsiddha@gmail.com \
--cc=torvalds@linux-foundation.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).