From mboxrd@z Thu Jan 1 00:00:00 1970 From: jistone@redhat.com (Josh Stone) Date: Mon, 22 Jun 2015 17:15:22 -0700 Subject: [PATCH] ARM: enable_irq before ret_fast_syscall tracing In-Reply-To: <1435018134-9653-1-git-send-email-jistone@redhat.com> References: <20150604100625.GI7557@n2100.arm.linux.org.uk> <1435018134-9653-1-git-send-email-jistone@redhat.com> Message-ID: <5588A51A.1080008@redhat.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On 06/22/2015 05:08 PM, Josh Stone wrote: > When reached via the slow path __sys_trace, __sys_trace_return and its > callees usually have interrupts still enabled. This is important if any > will schedule, like for a ptrace syscall-exit-stop. > > In the rarer case where tracing was not enabled on syscall entry, and > then ret_fast_syscall sees tracing was enabled mid-syscall, then it > also ought to branch to __sys_trace_return with interrupts enabled. Side note -- I haven't actually found any hard evidence that disabled interrupts here are a problem, even though it seems obviously bad. I used kprobes to confirm that I am indeed reaching this case, and modified my original testcase to spam this scenario in a loop. But I never encountered any instability or debug messages about interrupts. Still, it also runs cleanly with this patch, and I think this is more correct. Please correct me if I'm wrong! > Cc: Russell King > Signed-off-by: Josh Stone > --- > arch/arm/kernel/entry-common.S | 6 +++++- > 1 file changed, 5 insertions(+), 1 deletion(-) > > diff --git a/arch/arm/kernel/entry-common.S b/arch/arm/kernel/entry-common.S > index 4e7f40c577e6..5d8eb11b8571 100644 > --- a/arch/arm/kernel/entry-common.S > +++ b/arch/arm/kernel/entry-common.S > @@ -35,7 +35,7 @@ ret_fast_syscall: > disable_irq @ disable interrupts > ldr r1, [tsk, #TI_FLAGS] @ re-check for syscall tracing > tst r1, #_TIF_SYSCALL_WORK > - bne __sys_trace_return > + bne ret_fast_syscall_trace > tst r1, #_TIF_WORK_MASK > bne fast_work_pending > asm_trace_hardirqs_on > @@ -45,6 +45,10 @@ ret_fast_syscall: > ct_user_enter > > restore_user_regs fast = 1, offset = S_OFF > + > +ret_fast_syscall_trace: > + enable_irq @ enable interrupts > + b __sys_trace_return > UNWIND(.fnend ) > > /* >