[PATCH] ARM: enable_irq before ret_fast_syscall tracing
From: Josh Stone <hidden>
Date: 2015-06-23 00:15:22
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!
quoted hunk ↗ jump to hunk
Cc: Russell King <redacted> Signed-off-by: Josh Stone <redacted> --- 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 ) /*