[PATCH] ARM: enable_irq before ret_fast_syscall tracing
jistone at redhat.com
Mon Jun 22 17:15:22 PDT 2015
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 at arm.linux.org.uk>
> Signed-off-by: Josh Stone <jistone at 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
> @@ -45,6 +45,10 @@ ret_fast_syscall:
> restore_user_regs fast = 1, offset = S_OFF
> + enable_irq @ enable interrupts
> + b __sys_trace_return
> UNWIND(.fnend )
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