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tracing: Allocate the snapshot buffer before enabling probe

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Currently the snapshot trigger enables the probe and then allocates the
snapshot. If the probe triggers before the allocation, it could cause the
snapshot to fail and turn tracing off. It's best to allocate the snapshot
buffer first, and then enable the trigger. If something goes wrong in the
enabling of the trigger, the snapshot buffer is still allocated, but it can
also be freed by the user by writting zero into the snapshot buffer file.

Also add a check of the return status of alloc_snapshot().

Cc: stable@vger.kernel.org
Fixes: 77fd5c15e3 ("tracing: Add snapshot trigger to function probes")
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
This commit is contained in:
Steven Rostedt (VMware) 2017-04-19 12:07:08 -04:00
parent 9ed19c7695
commit df62db5be2
1 changed files with 5 additions and 3 deletions
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8
kernel/trace/trace.c
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@ -6733,11 +6733,13 @@ ftrace_trace_snapshot_callback(struct ftrace_hash *hash,
return ret;
out_reg:
ret = alloc_snapshot(&global_trace);
if (ret < 0)
goto out;
ret = register_ftrace_function_probe(glob, ops, count);
if (ret >= 0)
alloc_snapshot(&global_trace);
out:
return ret < 0 ? ret : 0;
}