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    SubjectRe: [PATCH tracing/kprobes 2/6] ftrace: Fix trace_add_event_call() to initialize list
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    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.


    > 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);

    But this I can see is needed ;-)

    -- Steve

    > + return ret;
    > }
    >
    > /* Add an additional event_call dynamically */
    >
    >



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