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    Subject[PATCH tracing/kprobes 2/6] ftrace: Fix trace_add_event_call() to initialize list take 2
    Steven Rostedt wrote:
    > On Wed, 2009-09-16 at 10:17 -0400, Masami Hiramatsu wrote:
    >> Steven Rostedt wrote:
    >
    >>>> diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
    >>>> index ba34920..38e82a5 100644
    >>>> --- a/kernel/trace/trace_events.c
    >>>> +++ b/kernel/trace/trace_events.c
    >>>> @@ -1009,10 +1009,14 @@ static int __trace_add_event_call(struct ftrace_event_call *call)
    >>>> if (!d_events)
    >>>> return -ENOENT;
    >>>>
    >>>> + INIT_LIST_HEAD(&call->list);
    >>>
    >>> The INIT_LIST_HEAD is not needed here. The list_add will assign it.
    >>
    >> Without initializing it, list debugging code warns always :-)
    >> Please see, __list_add()@lib/list_debug.c
    >
    > /me looks
    >
    > from: include/linux/list.h
    >
    > static inline void list_add(struct list_head *new, struct list_head *head)
    > {
    > __list_add(new, head, head->next);
    > }
    >
    > from: lib/list_debug.c
    >
    > void __list_add(struct list_head *new,
    > struct list_head *prev,
    > struct list_head *next)
    > {
    > WARN(next->prev != prev,
    > "list_add corruption. next->prev should be "
    > "prev (%p), but was %p. (next=%p).\n",
    > prev, next->prev, next);
    > WARN(prev->next != next,
    > "list_add corruption. prev->next should be "
    > "next (%p), but was %p. (prev=%p).\n",
    > next, prev->next, prev);
    > next->prev = new;
    > new->next = next;
    > new->prev = prev;
    > prev->next = new;
    > }
    >
    > What you pass in is:
    >
    > list_add(&call->list,&ftrace_events);
    >
    > new =&call->list;
    > prev =&ftrace_events->prev;
    > next =&ftrace_events->next;
    >
    > The above code never tests "new". The INIT_LIST_HEAD is useless.

    Oh, I see, I misunderstood. Thank you for pointing it out. :)
    Here, I updated the patch.

    ---
    ftrace: Fix trace_add_event_call() to initialize list

    From: Masami Hiramatsu <mhiramat@redhat.com>

    Handle failuer path in trace_add_event_call() for fixing below bug
    which occurred when I tried to add invalid event twice.

    Could not create debugfs 'kmalloc' directory
    Failed to register kprobe event: kmalloc
    Faild to register probe event(-1)
    ------------[ cut here ]------------
    WARNING: at /home/mhiramat/ksrc/random-tracing/lib/list_debug.c:26
    __list_add+0x27/0x5c()
    Hardware name:
    list_add corruption. next->prev should be prev (c07d78cc), but was
    00001000. (next=d854236c).
    Modules linked in: sunrpc uinput virtio_net virtio_balloon i2c_piix4 pcspkr
    i2c_core virtio_blk virtio_pci virtio_ring virtio [last unloaded:
    scsi_wait_scan]
    Pid: 1394, comm: tee Not tainted 2.6.31-rc9 #51
    Call Trace:
    [<c0438424>] warn_slowpath_common+0x65/0x7c
    [<c05371b3>] ? __list_add+0x27/0x5c
    [<c043846f>] warn_slowpath_fmt+0x24/0x27
    [<c05371b3>] __list_add+0x27/0x5c
    [<c047f050>] list_add+0xa/0xc
    [<c047f8f5>] trace_add_event_call+0x60/0x97
    [<c0483133>] command_trace_probe+0x42c/0x51b
    [<c044a1b3>] ? remove_wait_queue+0x22/0x27
    [<c042a9c0>] ? __wake_up+0x32/0x3b
    [<c04832f6>] probes_write+0xd4/0x10a
    [<c0483222>] ? probes_write+0x0/0x10a
    [<c04b27a9>] vfs_write+0x80/0xdf
    [<c04b289c>] sys_write+0x3b/0x5d
    [<c0670d41>] syscall_call+0x7/0xb
    ---[ end trace 2b962b5dc1fdc07d ]---

    Signed-off-by: Masami Hiramatsu <mhiramat@redhat.com>
    Cc: Jim Keniston <jkenisto@us.ibm.com>
    Cc: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
    Cc: Andi Kleen <ak@linux.intel.com>
    Cc: Christoph Hellwig <hch@infradead.org>
    Cc: Frank Ch. Eigler <fche@redhat.com>
    Cc: Frederic Weisbecker <fweisbec@gmail.com>
    Cc: H. Peter Anvin <hpa@zytor.com>
    Cc: Ingo Molnar <mingo@elte.hu>
    Cc: Jason Baron <jbaron@redhat.com>
    Cc: K.Prasad <prasad@linux.vnet.ibm.com>
    Cc: Lai Jiangshan <laijs@cn.fujitsu.com>
    Cc: Li Zefan <lizf@cn.fujitsu.com>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
    Cc: Steven Rostedt <rostedt@goodmis.org>
    Cc: Tom Zanussi <tzanussi@gmail.com>
    ---

    kernel/trace/trace_events.c | 5 ++++-
    1 files changed, 4 insertions(+), 1 deletions(-)


    diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
    index ba34920..83cc2c0 100644
    --- a/kernel/trace/trace_events.c
    +++ b/kernel/trace/trace_events.c
    @@ -1010,9 +1010,12 @@ static int __trace_add_event_call(struct ftrace_event_call *call)
    return -ENOENT;

    list_add(&call->list, &ftrace_events);
    - return event_create_dir(call, d_events, &ftrace_event_id_fops,
    + ret = event_create_dir(call, d_events, &ftrace_event_id_fops,
    &ftrace_enable_fops, &ftrace_event_filter_fops,
    &ftrace_event_format_fops);
    + if (ret < 0)
    + list_del(&call->list);
    + return ret;
    }

    /* Add an additional event_call dynamically */

    --
    Masami Hiramatsu

    Software Engineer
    Hitachi Computer Products (America), Inc.
    Software Solutions Division

    e-mail: mhiramat@redhat.com



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