[tip:x86/fpu] x86/fpu: Don't reset thread.fpu_counter

From: tip-bot for Oleg Nesterov
Date: Thu Feb 19 2015 - 06:32:44 EST

Commit-ID: a9241ea5fd709fc935dade130f4e3b2612bbe9e3
Gitweb: http://git.kernel.org/tip/a9241ea5fd709fc935dade130f4e3b2612bbe9e3
Author: Oleg Nesterov <oleg@xxxxxxxxxx>
AuthorDate: Fri, 6 Feb 2015 15:01:58 -0500
Committer: Borislav Petkov <bp@xxxxxxx>
CommitDate: Thu, 19 Feb 2015 11:12:40 +0100

x86/fpu: Don't reset thread.fpu_counter

The "else" branch clears ->fpu_counter as a remnant of the lazy FPU
usage counting:

e07e23e1fd30 ("[PATCH] non lazy "sleazy" fpu implementation")

However, switch_fpu_prepare() does this now so that else branch is

If we do use_eager_fpu(), then this has no effect. Otherwise, if we
actually wanted to prevent fpu preload after the context switch we would
need to reset it unconditionally, even if __thread_has_fpu().

Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>
Signed-off-by: Rik van Riel <riel@xxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/1423252925-14451-2-git-send-email-riel@xxxxxxxxxx
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
arch/x86/kernel/i387.c | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/arch/x86/kernel/i387.c b/arch/x86/kernel/i387.c
index a9a4229..4d0db9e 100644
--- a/arch/x86/kernel/i387.c
+++ b/arch/x86/kernel/i387.c
@@ -108,8 +108,7 @@ void unlazy_fpu(struct task_struct *tsk)
if (__thread_has_fpu(tsk)) {
- } else
- tsk->thread.fpu_counter = 0;
+ }
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/