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From: Adhemerval Zanella <adhemerval.zanella@linaro.org>
To: Florian Weimer <fweimer@redhat.com>,
	Adhemerval Zanella via Libc-alpha <libc-alpha@sourceware.org>
Subject: Re: [PATCH v2 2/9] nptl: Deallocate the thread stack on setup failure (BZ #19511)
Date: Tue, 1 Jun 2021 10:08:15 -0300	[thread overview]
Message-ID: <69aac17c-75e1-5b80-7df7-1dc09dea18b4@linaro.org> (raw)
In-Reply-To: <87r1hm6l4g.fsf@oldenburg.str.redhat.com>



On 01/06/2021 05:32, Florian Weimer wrote:
> * Adhemerval Zanella via Libc-alpha:
> 
>> @@ -424,17 +409,22 @@ start_thread (void *arg)
>>  	 have ownership (see CONCURRENCY NOTES above).  */
>>        if (__glibc_unlikely (pd->stopped_start))
>>  	{
>>  	  /* Get the lock the parent locked to force synchronization.  */
>>  	  lll_lock (pd->lock, LLL_PRIVATE);
>>  
>>  	  /* We have ownership of PD now.  */
>> +	  if (pd->setup_failed == 1)
>> +	    {
>> +	      /* In the case of a failed setup, the created thread will be
>> +		 responsible to free up the allocated resources.  The
>> +		 detached mode ensure it won't be joined and it will trigger
>> +		 the required cleanup.  */
>> +	      pd->joinid = pd;
>> +	      __do_cancel ();
>> +	    }
>>  
>>  	  /* And give it up right away.  */
>>  	  lll_unlock (pd->lock, LLL_PRIVATE);
>>  	}
> 
> I don't think this is quite right.  The failed thread should not linger
> around after pthread_create has reported failure to the caller.  It's
> better than what we had before, so maybe we should use this version and
> clean it up further later.

Agreed, but I think this is really an improvement over current strategy
as I commented earlier [1].  I think to proper fix would move the
lock prior any initialization so we don't need to run any unwinding
operations, skip directly to INTERNAL_SYSCALL_CALL (exit, 0), and let the
parent join the thread and do the resource deallocation.

> 
> At the point of the __do_cancel call, unwinding may not yet initialized,
> so the implied dlopen happens on a potentially very small stack.  It
> should be possible to replace it with a goto to the cleanup code.  Or
> maybe put the cleanup code into a separate function and call it here and
> on the regular cleanup path.
> 
> Apart from that, it looks fine to me.

The __do_cancel is not done really in asynchronous mode, so it will use
the allocated thread stack for the dlopen.  But I think with a better
strategy to move the 'struct thread' lock earlier than any initialization
will avoid such issue.

> 
> Thanks,
> Florian
> 

[1] https://sourceware.org/pipermail/libc-alpha/2021-May/126879.html

  reply	other threads:[~2021-06-01 13:08 UTC|newest]

Thread overview: 49+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-05-27 17:28 [PATCH v2 0/9] nptl: pthread cancellation refactor Adhemerval Zanella
2021-05-27 17:28 ` [PATCH v2 1/9] nptl: Remove exit-thread.h Adhemerval Zanella
2021-06-01  7:51   ` Florian Weimer
2021-06-01 12:55     ` Adhemerval Zanella
2021-05-27 17:28 ` [PATCH v2 2/9] nptl: Deallocate the thread stack on setup failure (BZ #19511) Adhemerval Zanella
2021-06-01  8:32   ` Florian Weimer
2021-06-01 13:08     ` Adhemerval Zanella [this message]
2021-06-01 13:55       ` Adhemerval Zanella
2021-06-02 12:56   ` [PATCH v3] " Adhemerval Zanella
2021-06-02 13:08     ` Andreas Schwab
2021-06-02 13:39       ` Adhemerval Zanella
2021-06-02 13:41         ` Andreas Schwab
2021-06-02 14:01           ` Adhemerval Zanella
2021-06-02 14:07             ` Andreas Schwab
2021-06-02 14:15               ` Adhemerval Zanella
2021-06-02 14:30                 ` Andreas Schwab
2021-06-02 14:42                   ` Adhemerval Zanella
2021-06-02 18:20               ` Joseph Myers
2021-06-02 18:30                 ` Florian Weimer
2021-06-02 19:02                   ` Adhemerval Zanella
2021-06-02 19:11                     ` Florian Weimer
2021-06-08 10:56     ` Florian Weimer
2021-06-08 17:01       ` Adhemerval Zanella
2021-06-09 13:49         ` Florian Weimer
2021-06-09 17:07           ` Adhemerval Zanella
2021-05-27 17:28 ` [PATCH v2 3/9] nptl: Install cancellation handler on pthread_cancel Adhemerval Zanella
2021-05-31 18:18   ` Adhemerval Zanella
2021-06-01  8:38     ` Florian Weimer
2021-06-01 13:10       ` Adhemerval Zanella
2021-06-01  8:39   ` Florian Weimer
2021-05-27 17:28 ` [PATCH v2 4/9] nptl: Remove CANCELING_BITMASK Adhemerval Zanella
2021-06-01  9:03   ` Florian Weimer
2021-06-01 13:50     ` Adhemerval Zanella
2021-06-01 16:36       ` Adhemerval Zanella
2021-05-27 17:28 ` [PATCH v2 5/9] nptl: Move cancel state out of cancelhandling Adhemerval Zanella
2021-06-01  9:58   ` Florian Weimer
2021-06-02 13:09     ` Adhemerval Zanella
2021-05-27 17:28 ` [PATCH v2 6/9] nptl: Move cancel type " Adhemerval Zanella
2021-06-01 12:37   ` Florian Weimer
2021-06-02 13:11     ` Adhemerval Zanella
2021-06-09 17:06       ` Adhemerval Zanella
2021-05-27 17:28 ` [PATCH v2 7/9] nptl: Implement raise in terms of pthread_kill Adhemerval Zanella
2021-06-01 12:40   ` Florian Weimer
2021-06-02 13:14     ` Adhemerval Zanella
2021-05-27 17:28 ` [PATCH v2 8/9] nptl: Use pthread_kill on pthread_cancel Adhemerval Zanella
2021-06-01 12:41   ` Florian Weimer
2021-05-27 17:28 ` [PATCH v2 9/9] nptl: Avoid async cancellation to wrongly update __nptl_nthreads (BZ #19366) Adhemerval Zanella
2021-06-01 14:29   ` Florian Weimer
2021-06-02 13:15     ` Adhemerval Zanella

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