linux-kernel - [PATCH 2/3] x86: make 64 bit ret_from_fork a little more similar to 32 bit

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Message-ID: <1311588187-20079-2-git-send-email-ian.campbell@citrix.com>
Date:	Mon, 25 Jul 2011 11:03:06 +0100
From:	Ian Campbell <ian.campbell@...rix.com>
To:	linux-kernel@...r.kernel.org
CC:	Pekka Enberg <penberg@...nel.org>,
	Cyrill Gorcunov <gorcunov@...il.com>,
	"H. Peter Anvin" <hpa@...or.com>, Andi Kleen <ak@...ux.intel.com>,
	Ian Campbell <ian.campbell@...rix.com>, x86@...nel.org
Subject: [PATCH 2/3] x86: make 64 bit ret_from_fork a little more similar to 32 bit

The 64 bit version resets EFLAGS before calling schedule_tail() and
therefore leaves EFLAGS.IF clear. 32 bit resets EFLAGS after calling
schedule_tail() and therefore leaves EFLAGS.IF set. I don't think
there is any practical difference between the two approaches since
interrupts are actually reenabled within schedule_tail
(schedule_tail->finish_task_switch->finish_lock_switch->raw_spin_unlock_irq->...->local_irq_enable)
so arbitrarily pick the 32 bit version and make 64 bit look like that.

Signed-off-by: Ian Campbell <ian.campbell@...rix.com>
Reviewed-by: Pekka Enberg <penberg@...nel.org>
Acked-by: Cyrill Gorcunov <gorcunov@...il.com>
Cc: x86@...nel.org
---
 arch/x86/kernel/entry_64.S |    7 ++++---
 1 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
index b50d142..9c28bd5 100644
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -394,13 +394,14 @@ END(save_paranoid)
 ENTRY(ret_from_fork)
 	DEFAULT_FRAME
 
-	LOCK ; btr $TIF_FORK,TI_flags(%r8)
 
-	pushq_cfi $0x0002
-	popfq_cfi				# reset kernel eflags
+	LOCK ; btr $TIF_FORK,TI_flags(%r8)
 
 	call schedule_tail			# rdi: 'prev' task parameter
 
+	pushq_cfi $0x0202
+	popfq_cfi				# reset kernel eflags
+
 	GET_THREAD_INFO(%rcx)
 
 	RESTORE_REST
-- 
1.7.2.5

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