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Subject[tip:tracing/blktrace] blktrace: fix blk_probes_ref chaos
Commit-ID:  2311b67256cb376cdbb541c781b95397f6896911
Gitweb: http://git.kernel.org/tip/2311b67256cb376cdbb541c781b95397f6896911
Author: Li Zefan <lizf@cn.fujitsu.com>
AuthorDate: Fri, 27 Mar 2009 10:20:09 +0800
Committer: Ingo Molnar <mingo@elte.hu>
CommitDate: Sat, 28 Mar 2009 12:51:41 +0100

blktrace: fix blk_probes_ref chaos

Impact: fix mixed ioctl and ftrace-plugin blktrace use refcount bugs

ioctl-based blktrace allocates bt and registers tracepoints when
ioctl(BLKTRACESETUP), and do all cleanups when ioctl(BLKTRACETEARDOWN).

while ftrace-based blktrace allocates/frees bt when:
# echo 1/0 > /sys/block/sda/sda1/trace/enable
and registers/unregisters tracepoints when:
# echo blk/nop > /debugfs/tracing/current_tracer
or
# echo 1/0 > /debugfs/tracing/tracing_enable
The separatation of allocation and registeration causes 2 problems:

1. current user-space blktrace still calls ioctl(TEARDOWN) when
ioctl(SETUP) failed:
# echo 1 > /sys/block/sda/sda1/trace/enable
# blktrace /dev/sda
BLKTRACESETUP: Device or resource busy
^C
and now blk_probes_ref == -1
2. Another way to make blk_probes_ref == -1:
# plugin sdb && mount sdb1
# echo 1 > /sys/block/sdb/sdb1/trace/enable
# remove sdb
This patch does the allocation and registeration when writing
sdaX/trace/enable.

Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
Cc: Jens Axboe <jens.axboe@oracle.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
LKML-Reference: <49CC37D9.6030201@cn.fujitsu.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>


---
kernel/trace/blktrace.c | 15 +++++++--------
1 files changed, 7 insertions(+), 8 deletions(-)
diff --git a/kernel/trace/blktrace.c b/kernel/trace/blktrace.c
index 5b28f0f..8d6bd12 100644
--- a/kernel/trace/blktrace.c
+++ b/kernel/trace/blktrace.c
@@ -478,7 +478,7 @@ int do_blk_trace_setup(struct request_queue *q, char *name, dev_t dev,
goto err;
}

- if (atomic_add_return(1, &blk_probes_ref) == 1)
+ if (atomic_inc_return(&blk_probes_ref) == 1)
blk_register_tracepoints();

return 0;
@@ -1091,8 +1091,6 @@ static void blk_tracer_print_header(struct seq_file *m)

static void blk_tracer_start(struct trace_array *tr)
{
- if (atomic_add_return(1, &blk_probes_ref) == 1)
- blk_register_tracepoints();
trace_flags &= ~TRACE_ITER_CONTEXT_INFO;
}

@@ -1107,15 +1105,10 @@ static int blk_tracer_init(struct trace_array *tr)
static void blk_tracer_stop(struct trace_array *tr)
{
trace_flags |= TRACE_ITER_CONTEXT_INFO;
- if (atomic_dec_and_test(&blk_probes_ref))
- blk_unregister_tracepoints();
}

static void blk_tracer_reset(struct trace_array *tr)
{
- if (!atomic_read(&blk_probes_ref))
- return;
-
blk_tracer_enabled = false;
blk_tracer_stop(tr);
}
@@ -1254,6 +1247,9 @@ static int blk_trace_remove_queue(struct request_queue *q)
if (bt == NULL)
return -EINVAL;

+ if (atomic_dec_and_test(&blk_probes_ref))
+ blk_unregister_tracepoints();
+
kfree(bt);
return 0;
}
@@ -1280,6 +1276,9 @@ static int blk_trace_setup_queue(struct request_queue *q, dev_t dev)
return -EBUSY;
}

+ if (atomic_inc_return(&blk_probes_ref) == 1)
+ blk_register_tracepoints();
+
return 0;
}


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