linux-kernel - [tip: x86/fpu] x86/fpu: Don't set TIF_NEED_FPU_LOAD for PF_IO

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Date:   Wed, 25 Jan 2023 11:39:12 -0000
From:   "tip-bot2 for Jens Axboe" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Jens Axboe <axboe@...nel.dk>, Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [tip: x86/fpu] x86/fpu: Don't set TIF_NEED_FPU_LOAD for PF_IO_WORKER threads

The following commit has been merged into the x86/fpu branch of tip:

Commit-ID:     cb3ea4b7671b7cfbac3ee609976b790aebd0bbda
Gitweb:        https://git.kernel.org/tip/cb3ea4b7671b7cfbac3ee609976b790aebd0bbda
Author:        Jens Axboe <axboe@...nel.dk>
AuthorDate:    Tue, 24 Jan 2023 08:23:20 -07:00
Committer:     Ingo Molnar <mingo@...nel.org>
CommitterDate: Wed, 25 Jan 2023 12:35:15 +01:00

x86/fpu: Don't set TIF_NEED_FPU_LOAD for PF_IO_WORKER threads

We don't set it on PF_KTHREAD threads as they never return to userspace,
and PF_IO_WORKER threads are identical in that regard. As they keep
running in the kernel until they die, skip setting the FPU flag on them.

More of a cosmetic thing that was found while debugging and
issue and pondering why the FPU flag is set on these threads.

Signed-off-by: Jens Axboe <axboe@...nel.dk>
Signed-off-by: Ingo Molnar <mingo@...nel.org>
Acked-by: Peter Zijlstra <peterz@...radead.org>
Link: https://lore.kernel.org/r/560c844c-f128-555b-40c6-31baff27537f@kernel.dk
---
 arch/x86/include/asm/fpu/sched.h | 2 +-
 arch/x86/kernel/fpu/context.h    | 2 +-
 arch/x86/kernel/fpu/core.c       | 2 +-
 3 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/x86/include/asm/fpu/sched.h b/arch/x86/include/asm/fpu/sched.h
index b2486b2..c2d6cd7 100644
--- a/arch/x86/include/asm/fpu/sched.h
+++ b/arch/x86/include/asm/fpu/sched.h
@@ -39,7 +39,7 @@ extern void fpu_flush_thread(void);
 static inline void switch_fpu_prepare(struct fpu *old_fpu, int cpu)
 {
 	if (cpu_feature_enabled(X86_FEATURE_FPU) &&
-	    !(current->flags & PF_KTHREAD)) {
+	    !(current->flags & (PF_KTHREAD | PF_IO_WORKER))) {
 		save_fpregs_to_fpstate(old_fpu);
 		/*
 		 * The save operation preserved register state, so the
diff --git a/arch/x86/kernel/fpu/context.h b/arch/x86/kernel/fpu/context.h
index 958accf..9fcfa5c 100644
--- a/arch/x86/kernel/fpu/context.h
+++ b/arch/x86/kernel/fpu/context.h
@@ -57,7 +57,7 @@ static inline void fpregs_restore_userregs(void)
 	struct fpu *fpu = &current->thread.fpu;
 	int cpu = smp_processor_id();
 
-	if (WARN_ON_ONCE(current->flags & PF_KTHREAD))
+	if (WARN_ON_ONCE(current->flags & (PF_KTHREAD | PF_IO_WORKER)))
 		return;
 
 	if (!fpregs_state_valid(fpu, cpu)) {
diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
index 9baa89a..2babc53 100644
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -426,7 +426,7 @@ void kernel_fpu_begin_mask(unsigned int kfpu_mask)
 
 	this_cpu_write(in_kernel_fpu, true);
 
-	if (!(current->flags & PF_KTHREAD) &&
+	if (!(current->flags & (PF_KTHREAD | PF_IO_WORKER)) &&
 	    !test_thread_flag(TIF_NEED_FPU_LOAD)) {
 		set_thread_flag(TIF_NEED_FPU_LOAD);
 		save_fpregs_to_fpstate(&current->thread.fpu);