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x86: Call fixup_exception() before notify_die() in math_error()

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fpu__drop() has an explicit fwait which under some conditions can trigger a
fixable FPU exception while in kernel. Thus, we should attempt to fixup the
exception first, and only call notify_die() if the fixup failed just like
in do_general_protection(). The original call sequence incorrectly triggers
KDB entry on debug kernels under particular FPU-intensive workloads.

Andy noted, that this makes the whole conditional irq enable thing even
more inconsistent, but fixing that it outside the scope of this.

Signed-off-by: Siarhei Liakh <siarhei.liakh@concurrent-rt.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Andy Lutomirski <luto@kernel.org>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: "Borislav  Petkov" <bpetkov@suse.de>
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/DM5PR11MB201156F1CAB2592B07C79A03B17D0@DM5PR11MB2011.namprd11.prod.outlook.com
This commit is contained in:
Siarhei Liakh 2018-06-14 19:36:07 +00:00 committed by Thomas Gleixner
parent 1d9f3e20a5
commit 3ae6295ccb
1 changed files with 8 additions and 6 deletions
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10
arch/x86/kernel/traps.c
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@ -834,16 +834,18 @@ static void math_error(struct pt_regs *regs, int error_code, int trapnr)
char *str = (trapnr == X86_TRAP_MF) ? "fpu exception" :
"simd exception";
if (notify_die(DIE_TRAP, str, regs, error_code, trapnr, SIGFPE) == NOTIFY_STOP)
return;
cond_local_irq_enable(regs);
if (!user_mode(regs)) {
if (!fixup_exception(regs, trapnr)) {
if (fixup_exception(regs, trapnr))
return;
task->thread.error_code = error_code;
task->thread.trap_nr = trapnr;
if (notify_die(DIE_TRAP, str, regs, error_code,
trapnr, SIGFPE) != NOTIFY_STOP)
die(str, regs, error_code);
}
return;
}