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    SubjectRe: [PATCH tracing/kprobes 2/6] ftrace: Fix trace_add_event_call() to initialize list
    Steven Rostedt wrote:
    > On Mon, 2009-09-14 at 16:49 -0400, Masami Hiramatsu wrote:
    >> Initialize event_call.list and 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 | 6 +++++-
    >> 1 files changed, 5 insertions(+), 1 deletions(-)
    >>
    >> 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

    Thank you,


    --
    Masami Hiramatsu

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

    e-mail: mhiramat@redhat.com



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