tracing: Comment why cond_snapshot is checked outside of max_lock protection

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Before setting tr->cond_snapshot, it must be NULL before it can be updated.
It can go to NULL when a trace event hist trigger is created or removed, and
can only be modified under the max_lock spin lock. But because it can only
be set to something other than NULL under both the max_lock spin lock as
well as the trace_types_lock, we can perform the check if it is not NULL
only under the trace_types_lock and fail out without having to grab the
max_lock spin lock.

This is very subtle, and deserves a comment.

Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

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Steven Rostedt (VMware) 2019-02-14 18:45:21 -05:00

parent a3d86a4ad7

commit 1c347a94ca

1 changed files with 8 additions and 0 deletions

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kernel/trace/trace.c

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