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Tue, 29 Sep 2026 00:17:55 -0700 (PDT) From: "Mukesh Kumar Chaurasiya (IBM)" To: maddy@linux.ibm.com, mpe@ellerman.id.au, npiggin@gmail.com, chleroy@kernel.org, ritesh.list@gmail.com, sshegde@linux.ibm.com, mkchauras@gmail.com, ruanjinjie@huawei.com, tglx@kernel.org, mkchauras@linux.ibm.com, ryan.roberts@arm.com, linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org Subject: [PATCH] powerpc/syscall: Avoid atomic test_and_clear_thread_flag on fast path Date: Tue, 29 Sep 2026 12:47:44 +0530 Message-ID: <20260929071744.2965058-1-mkchauras@gmail.com> X-Mailer: git-send-email 2.55.0 X-Mailing-List: linuxppc-dev@lists.ozlabs.org List-Id: List-Help: List-Owner: List-Post: List-Archive: , List-Subscribe: , , List-Unsubscribe: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit In system_call_exception(), test_and_clear_thread_flag(TIF_SYSCALL_RET) performs an atomic bit test-and-clear operation on every system call entry. This introduces an unnecessary performance regression on the syscall fast path. Combine the TIF_SYSCALL_RET check with the unlikely error condition from syscall_enter_from_user_mode_randomize_stack() using non-atomic test_thread_flag(). If the flag is set or entry failed, only then clear the flag via clear_thread_flag() and return the error value. Signed-off-by: Mukesh Kumar Chaurasiya (IBM) --- arch/powerpc/kernel/syscall.c | 6 ++---- 1 file changed, 2 insertions(+), 4 deletions(-) diff --git a/arch/powerpc/kernel/syscall.c b/arch/powerpc/kernel/syscall.c index fbefe1927b10..8529827d697f 100644 --- a/arch/powerpc/kernel/syscall.c +++ b/arch/powerpc/kernel/syscall.c @@ -18,14 +18,12 @@ notrace long system_call_exception(struct pt_regs *regs, unsigned long r0) long ret; syscall_fn f; - if (unlikely(!syscall_enter_from_user_mode_randomize_stack(regs, &r0))) { + if (unlikely(!syscall_enter_from_user_mode_randomize_stack(regs, &r0) || + test_thread_flag(TIF_SYSCALL_RET))) { clear_thread_flag(TIF_SYSCALL_RET); return syscall_get_error(current, regs); } - if (unlikely(test_and_clear_thread_flag(TIF_SYSCALL_RET))) - return syscall_get_error(current, regs); - if (unlikely(r0 >= NR_syscalls)) { if (unlikely(trap_is_unsupported_scv(regs))) { /* Unsupported scv vector */ -- 2.55.0