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Commit 17ba97e3 authored by Li Zefan's avatar Li Zefan Committed by Ingo Molnar
Browse files

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: default avatarLi Zefan <lizf@cn.fujitsu.com>
Acked-by: default avatarJens 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>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 35ac51bf

kernel/trace/blktrace.c

+7 −8
Original line number Diff line number Diff line
@@ -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;

}