Oleg's commit f893959b ("x86/fpu: Don't abuse drop_init_fpu() in
flush_thread()") removed drop_init_fpu() usage from flush_thread.
This seems to break things for me - the Go 1.4 test suite fails all
over the place with floating point comparision errors (offending
commit found through bisection).
Note: used_math() looks at current, and should be switch to
tsk_used_math(tsk), but even with this I see test suite breakage.
The functional change was that flush_thread after f893959b only calls
restore_init_xstate when both !use_eager_fpu and !used_math are true.
drop_init_fpu (now fpu_reset_state) calls restore_init_xstate()
regardless of whether current used_math().
There was a lot of commentary on the initial patch - not sure I
understand it all. Happy to get some pointers or be pointed to a
better fix.
Signed-off-by: Bobby Powers <bobbypow...@gmail.com>
Cc: Oleg Nesterov <o...@redhat.com>
Cc: Borislav Petkov <b...@suse.de>
Cc: Ingo Molnar <mi...@kernel.org>
Cc: Andy Lutomirski <l...@amacapital.net>
Cc: Dave Hansen <dave.han...@intel.com>
Cc: Fenghua Yu <fenghua...@intel.com>
Cc: Linus Torvalds <torva...@linux-foundation.org>
Cc: Pekka Riikonen <priik...@iki.fi>
Cc: Quentin Casasnovas <quentin.casasno...@oracle.com>
Cc: Rik van Riel <r...@redhat.com>
Cc: Suresh Siddha <sbsid...@gmail.com>
---
arch/x86/kernel/process.c | 12 +++++++-----
1 file changed, 7 insertions(+), 5 deletions(-)
diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 8213da6..c820baf5 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -156,11 +156,13 @@ void flush_thread(void)
/* FPU state will be reallocated lazily at the first use. */
drop_fpu(tsk);
free_thread_xstate(tsk);
- } else if (!used_math()) {
- /* kthread execs. TODO: cleanup this horror. */
- if (WARN_ON(init_fpu(tsk)))
- force_sig(SIGKILL, tsk);
- user_fpu_begin();
+ } else {
+ if (!used_math()) {
+ /* kthread execs. TODO: cleanup this horror. */
+ if (WARN_ON(init_fpu(tsk)))
+ force_sig(SIGKILL, tsk);
+ user_fpu_begin();
+ }
restore_init_xstate();
}
}
--
2.3.6
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