linux-kernel - [tip:x86/urgent] x86/fpu: Always restore_xinit_state() when use_eager

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Message-ID: <tip-c88d47480d300eaad80c213d50c9bf6077fc49bc@git.kernel.org>
Date:	Wed, 6 May 2015 03:14:15 -0700
From:	tip-bot for Bobby Powers <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	sbsiddha@...il.com, mingo@...nel.org,
	quentin.casasnovas@...cle.com, bp@...e.de,
	torvalds@...ux-foundation.org, bp@...en8.de, fenghua.yu@...el.com,
	linux-kernel@...r.kernel.org, tglx@...utronix.de, riel@...hat.com,
	dave.hansen@...el.com, priikone@....fi, hpa@...or.com,
	luto@...capital.net, bobbypowers@...il.com, oleg@...hat.com
Subject: [tip:x86/urgent] x86/fpu: Always restore_xinit_state()
  when use_eager_cpu()

Commit-ID:  c88d47480d300eaad80c213d50c9bf6077fc49bc
Gitweb:     http://git.kernel.org/tip/c88d47480d300eaad80c213d50c9bf6077fc49bc
Author:     Bobby Powers <bobbypowers@...il.com>
AuthorDate: Mon, 27 Apr 2015 08:10:41 -0700
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Wed, 6 May 2015 11:22:03 +0200

x86/fpu: Always restore_xinit_state() when use_eager_cpu()

The following commit:

  f893959b0898 ("x86/fpu: Don't abuse drop_init_fpu() in flush_thread()")

removed drop_init_fpu() usage from flush_thread(). This seems to break
things for me - the Go 1.4 test suite fails all over the place with
floating point comparision errors (offending commit found through
bisection).

The functional change was that flush_thread() after this commit
only calls restore_init_xstate() when both use_eager_fpu() and
!used_math() are true. drop_init_fpu() (now fpu_reset_state()) calls
restore_init_xstate() regardless of whether current used_math() - apply
the same logic here.

Switch used_math() -> tsk_used_math(tsk) to consistently use the grabbed
tsk instead of current, like in the rest of flush_thread().

Tested-by: Dave Hansen <dave.hansen@...el.com>
Signed-off-by: Bobby Powers <bobbypowers@...il.com>
Signed-off-by: Borislav Petkov <bp@...e.de>
Acked-by: Oleg Nesterov <oleg@...hat.com>
Cc: Andy Lutomirski <luto@...capital.net>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Fenghua Yu <fenghua.yu@...el.com>
Cc: H. Peter Anvin <hpa@...or.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Pekka Riikonen <priikone@....fi>
Cc: Quentin Casasnovas <quentin.casasnovas@...cle.com>
Cc: Rik van Riel <riel@...hat.com>
Cc: Suresh Siddha <sbsiddha@...il.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Fixes: f893959b ("x86/fpu: Don't abuse drop_init_fpu() in flush_thread()")
Link: http://lkml.kernel.org/r/1430147441-9820-1-git-send-email-bobbypowers@gmail.com
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 arch/x86/kernel/process.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index bfc99b3..6e338e3 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -156,11 +156,13 @@ void flush_thread(void)
 		/* FPU state will be reallocated lazily at the first use. */
 		drop_fpu(tsk);
 		free_thread_xstate(tsk);
-	} else if (!used_math()) {
-		/* kthread execs. TODO: cleanup this horror. */
-		if (WARN_ON(init_fpu(tsk)))
-			force_sig(SIGKILL, tsk);
-		user_fpu_begin();
+	} else {
+		if (!tsk_used_math(tsk)) {
+			/* kthread execs. TODO: cleanup this horror. */
+			if (WARN_ON(init_fpu(tsk)))
+				force_sig(SIGKILL, tsk);
+			user_fpu_begin();
+		}
 		restore_init_xstate();
 	}
 }
--
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