Re: [RFC patch 19/21] LTTng Linux Kernel Trace Thread Flag x86

Mathieu Desnoyers
2009-03-15T20:09:04Z

* Frederic Weisbecker (fweisbec@gmail.com) wrote:
> On Sun, Mar 15, 2009 at 03:03:59PM -0400, Mathieu Desnoyers wrote:
> > Add a thread flag to activate system-wide syscall tracing.
> >
> > Make x86_64 support TIF_SYSCALL_TRACE async flag set in entry.S
>
>
> x86-32 :-)
>
>
> > When the flag is inactive upon syscall entry and concurrently activated before
> > exit, we seem to reach a state where the top of stack is incorrect upon return
> > to user space.
> >
> > Fix this by fixing the top of stack and jumping to int_ret_from_sys_call if we
> > detect that thread flags has been modified.
>
>
> I don't see where you do that. May be you forgot some parts that match your changelog?
>

Oh, I see. I moved the *.S modifications to the LTTng instrumentation
patches. Maybe those belong more to the kernel trace thread flags
patches. I'll move them and repost.

Thanks,

Mathieu

> >
> > We make sure that the thread flag read is coherent between our new test and the ALLWORK_MASK test by first saving it in a register used for both comparisons.
>
> Ditto.
>
> Thanks,
> Frederic.
>
> >
> > Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
> > CC: Andi Kleen <ak@muc.de>
> > CC: Thomas Gleixner <tglx@linutronix.de>
> > CC: Ingo Molnar <mingo@redhat.com>
> > CC: H. Peter Anvin <hpa@zytor.com>
> > ---
> > arch/x86/include/asm/thread_info.h | 9 ++++++---
> > arch/x86/kernel/entry_32.S | 3 ++-
> > 2 files changed, 8 insertions(+), 4 deletions(-)
> >
> > Index: linux-2.6-lttng/arch/x86/include/asm/thread_info.h
> > ===================================================================
> > --- linux-2.6-lttng.orig/arch/x86/include/asm/thread_info.h 2009-01-14 22:10:38.000000000 -0500
> > +++ linux-2.6-lttng/arch/x86/include/asm/thread_info.h 2009-01-14 22:25:08.000000000 -0500
> > @@ -79,6 +79,7 @@ struct thread_info {
> > #define TIF_SYSCALL_EMU 6 /* syscall emulation active */
> > #define TIF_SYSCALL_AUDIT 7 /* syscall auditing active */
> > #define TIF_SECCOMP 8 /* secure computing */
> > +#define TIF_KERNEL_TRACE 9 /* kernel trace active */
> > #define TIF_MCE_NOTIFY 10 /* notify userspace of an MCE */
> > #define TIF_NOTSC 16 /* TSC is not accessible in userland */
> > #define TIF_IA32 17 /* 32bit process */
> > @@ -102,6 +103,7 @@ struct thread_info {
> > #define _TIF_SYSCALL_EMU (1 << TIF_SYSCALL_EMU)
> > #define _TIF_SYSCALL_AUDIT (1 << TIF_SYSCALL_AUDIT)
> > #define _TIF_SECCOMP (1 << TIF_SECCOMP)
> > +#define _TIF_KERNEL_TRACE (1 << TIF_KERNEL_TRACE)
> > #define _TIF_MCE_NOTIFY (1 << TIF_MCE_NOTIFY)
> > #define _TIF_NOTSC (1 << TIF_NOTSC)
> > #define _TIF_IA32 (1 << TIF_IA32)
> > @@ -117,17 +119,18 @@ struct thread_info {
> >
> > /* work to do in syscall_trace_enter() */
> > #define _TIF_WORK_SYSCALL_ENTRY \
> > - (_TIF_SYSCALL_TRACE | _TIF_SYSCALL_EMU | \
> > + (_TIF_SYSCALL_TRACE | _TIF_KERNEL_TRACE | _TIF_SYSCALL_EMU | \
> > _TIF_SYSCALL_AUDIT | _TIF_SECCOMP | _TIF_SINGLESTEP)
> >
> > /* work to do in syscall_trace_leave() */
> > #define _TIF_WORK_SYSCALL_EXIT \
> > - (_TIF_SYSCALL_TRACE | _TIF_SYSCALL_AUDIT | _TIF_SINGLESTEP)
> > + (_TIF_SYSCALL_TRACE | _TIF_KERNEL_TRACE | _TIF_SYSCALL_AUDIT | \
> > + _TIF_SINGLESTEP)
> >
> > /* work to do on interrupt/exception return */
> > #define _TIF_WORK_MASK \
> > (0x0000FFFF & \
> > - ~(_TIF_SYSCALL_TRACE|_TIF_SYSCALL_AUDIT| \
> > + ~(_TIF_SYSCALL_TRACE|_TIF_KERNEL_TRACE|_TIF_SYSCALL_AUDIT| \
> > _TIF_SINGLESTEP|_TIF_SECCOMP|_TIF_SYSCALL_EMU))
> >
> > /* work to do on any return to user space */
> > Index: linux-2.6-lttng/arch/x86/kernel/entry_32.S
> > ===================================================================
> > --- linux-2.6-lttng.orig/arch/x86/kernel/entry_32.S 2009-01-14 22:22:40.000000000 -0500
> > +++ linux-2.6-lttng/arch/x86/kernel/entry_32.S 2009-01-14 22:25:44.000000000 -0500
> > @@ -571,7 +571,8 @@ END(syscall_trace_entry)
> > # perform syscall exit tracing
> > ALIGN
> > syscall_exit_work:
> > - testb $_TIF_WORK_SYSCALL_EXIT, %cl
> > + /* Note, _TIF_KERNEL_TRACE is bit number 9, and so it needs testw and not testb */
> > + testw $_TIF_WORK_SYSCALL_EXIT, %cx
> > jz work_pending
> > TRACE_IRQS_ON
> > ENABLE_INTERRUPTS(CLBR_ANY) # could let syscall_trace_leave() call
> >
> > --
> > Mathieu Desnoyers
> > OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68
>