Re: [PATCH] MIPS: process: Remove lazy context flags for new kernel thread

Thomas Bogendoerfer
2023-11-20T19:08:40Z

On Sat, Nov 18, 2023 at 04:36:45PM +0100, Aurelien Jarno wrote:
> > Anyway, I have been able to test a backport of the patch onto the 5.10
> > kernel (with minor adjustments) and I confirm it fixes the reported
> > issue.
> >
> > Tested-by: Aurelien Jarno <aurel32@debian.org>
>
> It seems that this patch hasn't been merged yet, either in Linus' tree
> or in the MIPS tree. Is there anything blocking?

sorry, took some time to get really back from vacation...

I don't like the patch doing too much code restructing. I can't
reproduce on my loongson machine, so I can't test below patch...

What cmake version do I need and what would be a package to
reproduce the bug ?

Thomas.

diff --git a/arch/mips/kernel/process.c b/arch/mips/kernel/process.c
index 5387ed0a5186..b630604c577f 100644
--- a/arch/mips/kernel/process.c
+++ b/arch/mips/kernel/process.c
@@ -121,6 +121,19 @@ int copy_thread(struct task_struct *p, const struct kernel_clone_args *args)
/* Put the stack after the struct pt_regs. */
childksp = (unsigned long) childregs;
p->thread.cp0_status = (read_c0_status() & ~(ST0_CU2|ST0_CU1)) | ST0_KERNEL_CUMASK;
+
+ /*
+ * New tasks lose permission to use the fpu. This accelerates context
+ * switching for most programs since they don't use the fpu.
+ */
+ clear_tsk_thread_flag(p, TIF_USEDFPU);
+ clear_tsk_thread_flag(p, TIF_USEDMSA);
+ clear_tsk_thread_flag(p, TIF_MSA_CTX_LIVE);
+
+#ifdef CONFIG_MIPS_MT_FPAFF
+ clear_tsk_thread_flag(p, TIF_FPUBOUND);
+#endif /* CONFIG_MIPS_MT_FPAFF */
+
if (unlikely(args->fn)) {
/* kernel thread */
unsigned long status = p->thread.cp0_status;
@@ -149,20 +162,8 @@ int copy_thread(struct task_struct *p, const struct kernel_clone_args *args)
p->thread.reg29 = (unsigned long) childregs;
p->thread.reg31 = (unsigned long) ret_from_fork;

- /*
- * New tasks lose permission to use the fpu. This accelerates context
- * switching for most programs since they don't use the fpu.
- */
childregs->cp0_status &= ~(ST0_CU2|ST0_CU1);

- clear_tsk_thread_flag(p, TIF_USEDFPU);
- clear_tsk_thread_flag(p, TIF_USEDMSA);
- clear_tsk_thread_flag(p, TIF_MSA_CTX_LIVE);
-
-#ifdef CONFIG_MIPS_MT_FPAFF
- clear_tsk_thread_flag(p, TIF_FPUBOUND);
-#endif /* CONFIG_MIPS_MT_FPAFF */
-
#ifdef CONFIG_MIPS_FP_SUPPORT
atomic_set(&p->thread.bd_emu_frame, BD_EMUFRAME_NONE);
#endif

--
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good idea. [ RFC1925, 2.3 ]