| Message ID | 1435018134-9653-1-git-send-email-jistone@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
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 <rmk+kernel@arm.linux.org.uk> > Signed-off-by: Josh Stone <jistone@redhat.com> > --- > 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 ) > > /* >
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 ) /*
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. Cc: Russell King <rmk+kernel@arm.linux.org.uk> Signed-off-by: Josh Stone <jistone@redhat.com> --- arch/arm/kernel/entry-common.S | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-)