psxcancel test failure

Sebastian Huber sebastian.huber at
Sat Mar 9 11:14:53 UTC 2013

Hello Joel,

I briefly look at the cancellation sequence but it seemed to be quite 
complex.  There is also a POSIX requirement that we don't meet at the 

"The cancellation processing in the target thread runs asynchronously 
with respect to the calling thread returning from /pthread_cancel()/. "

There is also a problem in pthread_cleanup_push().  It allocates memory 
from the workspace and fails silently in case this is not possible.  
POSIX allows this:

"These functions may be implemented as macros and will appear as 
statements and in pairs within the same lexical scope (that is, the 
/pthread_cleanup_push()/ macro may be thought to expand to a token list 
whose first token is *`{'* with /pthread_cleanup_pop()/ expanding to a 
token list whose last token is the corresponding *`}'*. "

So it is possible to place the control structure on the thread stack.

On 08/03/13 20:23, Joel Sherrill wrote:
> Hi
> Sebastian mentioned this failure to me privately and I have taken a first
> look at it.
> My impression is that the cancellation request is doing some thread exit
> work and then the thread calls pthread_exit() and does it again. The
> second time, it faults dereferencing a NULL pointer.
> I will think on it but a fix is likely not too hard. I just want to 
> understand
> the flow before I insert a NULL pointer check.

Sebastian Huber, embedded brains GmbH

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