Re: [PATCH v5 06/10] Uprobes: Support SDT markers having reference count (semaphore)
From: Ravi Bangoria
Date: Wed Jul 04 2018 - 05:24:44 EST
On 07/04/2018 02:46 PM, Srikar Dronamraju wrote:
>> I'm not sure if I get your concerns but let me try to explain what happens
>> in such cases. please let me know if I misunderstood your point.
>> 1. Install a probe using perf.
>> # ./perf probe sdt_tick:loop2
>> Does this explain your concerns?
> No, this was not my concern.
> My concern is with two users on the same USDT.
> 1. First user enables the probe point but doesn't increment the ref_cnt.
> via uprobe_register
> 2. Second user tries to enable the probe point and also increments the
> ref_cnt via uprobe_register_refctr.
Ok got it. uprobe_register_refctr() will return with error because we don't
allow one uprobe(inode+offset) with multiple reference counter.
i.e. If inode+offset matches for two uprobes, ref_ctr_offset must match as
well. Patch 8/10 takes care of this.
> 3. If the second user now removes the probe point via uprobe_unregister.
> 4. What is the state of the ref_cnt?
> Thanks and Regards