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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@redhat.com>
AuthorDate: Fri, 13 Mar 2015 18:30:30 +0100
Committer: Ingo Molnar <mingo@kernel.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@redhat.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Pekka Riikonen <priikone@iki.fi>
Cc: Quentin Casasnovas <quentin.casasnovas@oracle.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Suresh Siddha <sbsiddha@gmail.com>
Link: http://lkml.kernel.org/r/20150313173030.GA31217@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.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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