linux-kernel - [tip:x86/fpu] x86/fpu: Don't abuse drop_init_fpu() in flush

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Date:	Mon, 23 Mar 2015 05:21:37 -0700
From:	tip-bot for Oleg Nesterov <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	priikone@....fi, dave.hansen@...el.com, sbsiddha@...il.com,
	luto@...capital.net, tglx@...utronix.de,
	quentin.casasnovas@...cle.com, oleg@...hat.com,
	linux-kernel@...r.kernel.org, fenghua.yu@...el.com,
	torvalds@...ux-foundation.org, bp@...e.de, mingo@...nel.org,
	hpa@...or.com, riel@...hat.com
Subject: [tip:x86/fpu] x86/fpu: Don't abuse drop_init_fpu()
  in flush_thread()

Commit-ID:  f893959b0898bd876673adbeb6798bdf25c034d7
Gitweb:     http://git.kernel.org/tip/f893959b0898bd876673adbeb6798bdf25c034d7
Author:     Oleg Nesterov <oleg@...hat.com>
AuthorDate: Fri, 13 Mar 2015 18:30:30 +0100
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Mon, 23 Mar 2015 10:13:58 +0100

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

flush_thread() -> drop_init_fpu() is suboptimal and confusing. It does
drop_fpu() or restore_init_xstate() depending on !use_eager_fpu(). But
flush_thread() too checks eagerfpu right after that, and if it is true
then restore_init_xstate() just burns CPU for no reason. We are going to
load init_xstate_buf again after we set used_math()/user_has_fpu(), until
then the FPU state can't survive after switch_to().

Remove it, and change the "if (!use_eager_fpu())" to call drop_fpu().
While at it, clean up the tsk/current usage.

Signed-off-by: Oleg Nesterov <oleg@...hat.com>
Signed-off-by: Borislav Petkov <bp@...e.de>
Cc: Andy Lutomirski <luto@...capital.net>
Cc: Dave Hansen <dave.hansen@...el.com>
Cc: Fenghua Yu <fenghua.yu@...el.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>
Link: http://lkml.kernel.org/r/20150313173030.GA31217@redhat.com
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 arch/x86/kernel/process.c | 15 ++++++---------
 1 file changed, 6 insertions(+), 9 deletions(-)

diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 6b05829..1d2ebad 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -132,17 +132,14 @@ void flush_thread(void)
 	flush_ptrace_hw_breakpoint(tsk);
 	memset(tsk->thread.tls_array, 0, sizeof(tsk->thread.tls_array));
 
-	drop_init_fpu(tsk);
-	/*
-	 * Free the FPU state for non xsave platforms. They get reallocated
-	 * lazily at the first use.
-	 */
-	if (!use_eager_fpu())
+	if (!use_eager_fpu()) {
+		/* FPU state will be reallocated lazily at the first use. */
+		drop_fpu(tsk);
 		free_thread_xstate(tsk);
-	else if (!used_math()) {
+	} else if (!used_math()) {
 		/* kthread execs. TODO: cleanup this horror. */
-		if (WARN_ON(init_fpu(current)))
-			force_sig(SIGKILL, current);
+		if (WARN_ON(init_fpu(tsk)))
+			force_sig(SIGKILL, tsk);
 		user_fpu_begin();
 		restore_init_xstate();
 	}
--
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