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    SubjectRe: [PATCH 4/7] add syscall tracepoints
    On Fri, Jun 19, 2009 at 08:35:04AM -0400, Mathieu Desnoyers wrote:
    > * Frederic Weisbecker (fweisbec@gmail.com) wrote:
    > > On Fri, Jun 12, 2009 at 05:24:54PM -0400, Jason Baron wrote:
    > > >
    > > > add two tracepoints in syscall exit and entry path, conditioned on
    > > > TIF_SYSCALL_FTRACE. Supports the syscall trace event code.
    > > >
    > > >
    > > > Signed-off-by: Jason Baron <jbaron@redhat.com>
    > > >
    > > > ---
    > > > arch/x86/kernel/ptrace.c | 6 ++++--
    > > > include/trace/syscall.h | 18 ++++++++++++++++++
    > > > kernel/tracepoint.c | 38 ++++++++++++++++++++++++++++++++++++++
    > > > 3 files changed, 60 insertions(+), 2 deletions(-)
    > > >
    > > > diff --git a/arch/x86/kernel/ptrace.c b/arch/x86/kernel/ptrace.c
    > > > index 09ecbde..1c7301a 100644
    > > > --- a/arch/x86/kernel/ptrace.c
    > > > +++ b/arch/x86/kernel/ptrace.c
    > > > @@ -36,6 +36,8 @@
    > > > #include <asm/ds.h>
    > > >
    > > > #include <trace/syscall.h>
    > > > +DEFINE_TRACE(syscall_enter);
    > > > +DEFINE_TRACE(syscall_exit);
    > > >
    > > > #include "tls.h"
    > > >
    > > > @@ -1498,7 +1500,7 @@ asmregparm long syscall_trace_enter(struct pt_regs *regs)
    > > > ret = -1L;
    > > >
    > > > if (unlikely(test_thread_flag(TIF_SYSCALL_FTRACE)))
    > > > - ftrace_syscall_enter(regs);
    > > > + trace_syscall_enter(regs, regs->orig_ax);
    > > >
    > > > if (unlikely(current->audit_context)) {
    > > > if (IS_IA32)
    > > > @@ -1524,7 +1526,7 @@ asmregparm void syscall_trace_leave(struct pt_regs *regs)
    > > > audit_syscall_exit(AUDITSC_RESULT(regs->ax), regs->ax);
    > > >
    > > > if (unlikely(test_thread_flag(TIF_SYSCALL_FTRACE)))
    > > > - ftrace_syscall_exit(regs);
    > > > + trace_syscall_exit(regs, regs->ax);
    > > >
    > > > if (test_thread_flag(TIF_SYSCALL_TRACE))
    > > > tracehook_report_syscall_exit(regs, 0);
    > > > diff --git a/include/trace/syscall.h b/include/trace/syscall.h
    > > > index 8cfe515..d5d8310 100644
    > > > --- a/include/trace/syscall.h
    > > > +++ b/include/trace/syscall.h
    > > > @@ -2,6 +2,24 @@
    > > > #define _TRACE_SYSCALL_H
    > > >
    > > > #include <asm/ptrace.h>
    > > > +#include <linux/tracepoint.h>
    > > > +
    > > > +extern void syscall_regfunc(void);
    > > > +extern void syscall_unregfunc(void);
    > > > +
    > > > +DECLARE_TRACE_REG(syscall_enter,
    > > > + TP_PROTO(struct pt_regs *regs, long id),
    > > > + TP_ARGS(regs, id),
    > > > + syscall_regfunc,
    > > > + syscall_unregfunc
    > > > +);
    > > > +
    > > > +DECLARE_TRACE_REG(syscall_exit,
    > > > + TP_PROTO(struct pt_regs *regs, long ret),
    > > > + TP_ARGS(regs, ret),
    > > > + syscall_regfunc,
    > > > + syscall_unregfunc
    > > > +);
    > > >
    > > > /*
    > > > * A syscall entry in the ftrace syscalls array.
    > > > diff --git a/kernel/tracepoint.c b/kernel/tracepoint.c
    > > > index 1ef5d3a..5b34ff9 100644
    > > > --- a/kernel/tracepoint.c
    > > > +++ b/kernel/tracepoint.c
    > >
    > >
    > >
    > > At a first glance I wasn't sure tracepoint.c is the right
    > > place for these.
    > > But indeed putting those two callbacks here avoids any
    > > dependency to the syscall tracer when someone else needs
    > > the syscall tracepoints.
    > >
    > > Well, I guess we can keep them there.
    > >
    > >
    > >
    > > > @@ -24,6 +24,7 @@
    > > > #include <linux/tracepoint.h>
    > > > #include <linux/err.h>
    > > > #include <linux/slab.h>
    > > > +#include <linux/sched.h>
    > > >
    > > > extern struct tracepoint __start___tracepoints[];
    > > > extern struct tracepoint __stop___tracepoints[];
    > > > @@ -577,3 +578,40 @@ static int init_tracepoints(void)
    > > > __initcall(init_tracepoints);
    > > >
    > > > #endif /* CONFIG_MODULES */
    > > > +
    > > > +DEFINE_MUTEX(regfunc_mutex);
    > > > +int sys_tracepoint_refcount;
    > >
    > >
    > > Looks like regfunc_mutex is only there to protect
    > > sys_tracepoint_refcount. May be you can just make it atomic_t?
    > >
    >
    > Nope, regfunc_mutex makes sure there is no disable/enable occuring
    > concurrently. They only take a tasklist read lock, so they can happen
    > concurrently if it wasn't for the regfunc_mutex.
    >
    > Unless I'm missing something totally obvious about the refcount, the
    > mutex is needed, and there is no need to go for an atomic type in this
    > case.
    >
    > Thanks,
    >
    > Mathieu



    Ah...
    Eh, you're right :)

    Although concurrent enable/disable of the TIF flags would reveal a bug
    in the tracepoint user (enable and disable not serialized).

    But yeah let's keep it as a mutex.

    Thanks.


    > > Thanks,
    > > Frederic.
    > >
    > >
    > > > +
    > > > +void syscall_regfunc(void)
    > > > +{
    > > > + unsigned long flags;
    > > > + struct task_struct *g, *t;
    > > > +
    > > > + mutex_lock(&regfunc_mutex);
    > > > + if (!sys_tracepoint_refcount) {
    > > > + read_lock_irqsave(&tasklist_lock, flags);
    > > > + do_each_thread(g, t) {
    > > > + set_tsk_thread_flag(t, TIF_SYSCALL_FTRACE);
    > > > + } while_each_thread(g, t);
    > > > + read_unlock_irqrestore(&tasklist_lock, flags);
    > > > + }
    > > > + sys_tracepoint_refcount++;
    > > > + mutex_unlock(&regfunc_mutex);
    > > > +}
    > > > +
    > > > +void syscall_unregfunc(void)
    > > > +{
    > > > + unsigned long flags;
    > > > + struct task_struct *g, *t;
    > > > +
    > > > + mutex_lock(&regfunc_mutex);
    > > > + sys_tracepoint_refcount--;
    > > > + if (!sys_tracepoint_refcount) {
    > > > + read_lock_irqsave(&tasklist_lock, flags);
    > > > + do_each_thread(g, t) {
    > > > + clear_tsk_thread_flag(t, TIF_SYSCALL_FTRACE);
    > > > + } while_each_thread(g, t);
    > > > + read_unlock_irqrestore(&tasklist_lock, flags);
    > > > + }
    > > > + mutex_unlock(&regfunc_mutex);
    > > > +}
    > > > --
    > > > 1.6.0.6
    > > >
    > >
    >
    > --
    > Mathieu Desnoyers
    > OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68



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