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 <CADYN=9K1BdyupzcDAbyk2JTio1A98J9tsBS_LeOH4=GVG=7FqQ@mail.gmail.com> <871r5h7km4.ffs@tglx>
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From:   Anders Roxell <anders.roxell@linaro.org>
Date:   Wed, 22 Sep 2021 21:42:50 +0200
Message-ID: <CADYN=9LmxMAU7DPAQUZpHkXLPh8QJgrGT7qgd9SZ_80brfmfrQ@mail.gmail.com>
Subject: Re: [patch V3 15/20] x86/fpu/signal: Change return type of
 copy_fpregs_to_sigframe() helpers to boolean
To:     Thomas Gleixner <tglx@linutronix.de>
Cc:     LKML <linux-kernel@vger.kernel.org>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@kernel.org>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Tony Luck <tony.luck@intel.com>,
        Alexei Starovoitov <ast@kernel.org>,
        Peter Ziljstra <peterz@infradead.org>,
        Song Liu <songliubraving@fb.com>,
        Daniel Borkmann <daniel@iogearbox.net>
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Precedence: bulk

On Tue, 21 Sept 2021 at 22:13, Thomas Gleixner <tglx@linutronix.de> wrote:
>
> On Tue, Sep 21 2021 at 12:58, Anders Roxell wrote:
> > On Wed, 8 Sept 2021 at 15:30, Thomas Gleixner <tglx@linutronix.de> wrote:
> >>
> >> Now that copy_fpregs_to_sigframe() returns boolean the individual return
> >> codes in the related helper functions do not make sense anymore. Change
> >> them to return boolean success/fail.
> >>
> >> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> >
> > When I build and boot (qemu_x86_64) a defconfig kernel on from todays
> > next tag next-20210921 I see the following segmentation fault
> >
> > 2021-09-21T10:11:45 <6>[    1.622922] mount (89) used greatest stack
> > depth: 14384 bytes left
> > 2021-09-21T10:11:45 <6>[    1.664760] EXT4-fs (sda): re-mounted. Opts:
> > (null). Quota mode: none.
> > 2021-09-21T10:11:45 <6>[    1.691041] mkdir (92) used greatest stack
> > depth: 14312 bytes left
> > 2021-09-21T10:11:45 <6>[    1.713201] mount (93) used greatest stack
> > depth: 13720 bytes left
> > 2021-09-21T10:11:46 Starting syslogd: /etc/init.d/rcS: line 12:   101
> > Segmentation fault      $i start
> >
> >
> > I did a bisection and found this as the faulty patch [1]. When I
> > revert this patch I can't see the issue.
> >
> > We noticed that function 'save_xstate_epilog()' changes the polarity
> > of its return code for one of the return statements, and for its only
> > caller. but not for the other return statement.
> >
> > I tried this patch and I couldn't see the segmentation fault.
> >
> > diff --git a/arch/x86/kernel/fpu/signal.c b/arch/x86/kernel/fpu/signal.c
> > index 445c57c9c539..61eeebc04427 100644
> > --- a/arch/x86/kernel/fpu/signal.c
> > +++ b/arch/x86/kernel/fpu/signal.c
> > @@ -104,7 +104,7 @@ static inline int save_xstate_epilog(void __user
> > *buf, int ia32_frame)
> >         err = __copy_to_user(&x->i387.sw_reserved, sw_bytes, sizeof(*sw_bytes));
> >
> >         if (!use_xsave())
> > -               return err;
> > +               return !err;
>
> Oops. Good catch. Care to send a proper patch for this?

Yes I can try to do that.

Cheers,
Anders