[PATCH] nptl: Retry SIGSETXID delivery on EAGAIN in setxid (bug 21108)

[Adhemerval Zanella Netto]

On 10/06/26 11:20, Andreas Schwab wrote:
> On Jun 09 2026, Adhemerval Zanella wrote:
> 
>> @@ -150,31 +150,86 @@ setxid_unmark_thread (struct xid_command *cmdp, struct pthread *t)
>>  }
>>  
>>  
>> -static int
>> +enum setxid_signal_state
>> +{
>> +  setxid_signal_done,  /* Thread  has not finished starting or has already
>> +			  exited; ignore it.  */
>> +  setxid_signal_sent,  /* The signal was delivered and the thread signal
>> +			  handler will run (the xid_command::crnt was already
>> +			  incremented.  */
>> +  setxid_signal_retry, /* tgkill returned EAGAIN (the signal queue
>> +			  RLIMIT_SIGPENDING is full), the thread is still
>> +			  running and must be signal.  The caller has to
>                                               signaled
> 
>> +  /* The kernel might return EAGAIN for realtime signals if the signal queue
>> +     reaches its limits (RLIMIT_SIGPENDING) because tgkill does not use the
>> +     guaranteed-delivery override path as the kill syscall.  The threads is
>                                                                     thread
> 
>> +     still running and *must* process the credential change, so instruc the
>                                                                    instruct
> 
>> +/* The sexid is implemented on Linux with a SIGSETXID broadcast, and tgkill
>> +   might fail with EAGAIN if the signal queue is full (RLIMIT_SIGPENDING)
>> +   because SIGSETXID is a realtime signal.
>> +
>> +   The test first fills the queue, run the setresuid in a helper thread, and
>                                       runs
> 
>> +   verifiers that it does *not* complete while the queue is still full.
>       verifies
> 

Ack, fixed locally.