linux-kernel - [tip:x86/fpu] x86, fpu: copy_process: Sanitize fpu-> last

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Message-ID: <tip-5e23fee23ea10730c752edce1777e6b7e727290f@git.kernel.org>
Date:	Tue, 2 Sep 2014 15:19:30 -0700
From:	tip-bot for Oleg Nesterov <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, hpa@...or.com, mingo@...nel.org,
	sbsiddha@...il.com, oleg@...hat.com, tglx@...utronix.de,
	hpa@...ux.intel.com
Subject: [tip:x86/fpu] x86, fpu: copy_process: Sanitize fpu->
 last_cpu initialization

Commit-ID:  5e23fee23ea10730c752edce1777e6b7e727290f
Gitweb:     http://git.kernel.org/tip/5e23fee23ea10730c752edce1777e6b7e727290f
Author:     Oleg Nesterov <oleg@...hat.com>
AuthorDate: Tue, 2 Sep 2014 19:57:27 +0200
Committer:  H. Peter Anvin <hpa@...ux.intel.com>
CommitDate: Tue, 2 Sep 2014 14:51:16 -0700

x86, fpu: copy_process: Sanitize fpu->last_cpu initialization

Cosmetic, but imho memset(&dst->thread.fpu, 0) is not good simply
because it hides the (important) usage of ->has_fpu/etc from grep.
Change this code to initialize the members explicitly.

And note that ->last_cpu = 0 looks simply wrong, this can confuse
fpu_lazy_restore() if per_cpu(fpu_owner_task, 0) has already exited
and copy_process() re-allocated the same task_struct. Fortunately
this is not actually possible because child->fpu_counter == 0 and
thus fpu_lazy_restore() will not be called, but still this is not
clean/robust.

Signed-off-by: Oleg Nesterov <oleg@...hat.com>
Link: http://lkml.kernel.org/r/20140902175727.GA21666@redhat.com
Reviewed-by: Suresh Siddha <sbsiddha@...il.com>
Signed-off-by: H. Peter Anvin <hpa@...ux.intel.com>
---
 arch/x86/kernel/process.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index b9ba9d5..a44268c 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -66,7 +66,9 @@ int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src)
 {
 	*dst = *src;
 
-	memset(&dst->thread.fpu, 0, sizeof(dst->thread.fpu));
+	dst->thread.fpu.has_fpu = 0;
+	dst->thread.fpu.last_cpu = ~0;
+	dst->thread.fpu.state = NULL;
 	if (tsk_used_math(src)) {
 		int err = fpu_alloc(&dst->thread.fpu);
 		if (err)
--
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