1eaa4787a7
The flags variable is protected by the event_mutex when modifying, but the event_mutex is not held when reading the variable. This is due to the fact that the reads occur in critical sections where taking a mutex (or even a spinlock) is not wanted. But the two flags that exist (enable and filter_active) have the code written as such to handle the reads to not need a lock. The enable flag is used just to know if the event is enabled or not and its use is always under the event_mutex. Whether or not the event is actually enabled is really determined by the tracepoint being registered. The flag is just a way to let the code know if the tracepoint is registered. The filter_active is different. It is read without the lock. If it is set, then the event probes jump to the filter code. There can be a slight mismatch between filters available and filter_active. If the flag is set but no filters are available, the code safely jumps to a filter nop. If the flag is not set and the filters are available, then the filters are skipped. This is acceptable since filters are usually set before tracing or they are set by humans, which would not notice the slight delay that this causes. v2: Fixed typo: "cacheing" -> "caching" Reported-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Acked-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Cc: Tom Zanussi <tzanussi@gmail.com> Signed-off-by: Steven Rostedt <rostedt@goodmis.org> |
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| acpi | ||
| asm-generic | ||
| crypto | ||
| drm | ||
| keys | ||
| linux | ||
| math-emu | ||
| media | ||
| mtd | ||
| net | ||
| pcmcia | ||
| rdma | ||
| rxrpc | ||
| scsi | ||
| sound | ||
| trace | ||
| video | ||
| xen | ||
| Kbuild | ||