LIBC_PROBE and locks

[Carlos O'Donell]

On 11/17/2015 09:12 AM, Florian Weimer wrote:
> On 11/17/2015 05:20 AM, Carlos O'Donell wrote:
>> On 11/16/2015 12:54 PM, Florian Weimer wrote:
>>> Is it okay to call LIBC_PROBE while internal locks are held?  Or could
>>> this result in deadlocks by itself?  (I'm aware that the arguments are
>>> always evaluated.)
>>
>> How would it cause deadlocks? The external observer, say systemtap or
>> gdb, are outside of the process and should not modify the state of the
>> process in such a way as to cause a deadlock. Under what conditions might
>> the evaluation of the arguments cause a deadlock?
> 
> Are only external observers supported?  I wasn't sure if this is some
> sort of self-observing capability which is supposed to work, in which
> case this would be some sort of callback mechanism and subject to
> similar locking issues.
> 
> Frank tells me that self-inspection isn't supported, so my concern is
> unfounded.

Agreed. Self-inspection was not considered in the design. It gets
complicated really fast.

Cheers,
Carlos.