public inbox for libc-alpha@sourceware.org
 help / color / mirror / Atom feed
From: Florian Weimer <fweimer@redhat.com>
To: Adhemerval Zanella via Libc-alpha <libc-alpha@sourceware.org>
Subject: Re: [PATCH v2 4/9] nptl: Remove CANCELING_BITMASK
Date: Tue, 01 Jun 2021 11:03:23 +0200	[thread overview]
Message-ID: <87bl8q6jok.fsf@oldenburg.str.redhat.com> (raw)
In-Reply-To: <20210527172823.3461314-5-adhemerval.zanella@linaro.org> (Adhemerval Zanella via Libc-alpha's message of "Thu, 27 May 2021 14:28:18 -0300")

* Adhemerval Zanella via Libc-alpha:

> The CANCELING_BITMASK is used as an optimization to avoid sending
> the signal when pthread_cancel is called in a concurrent manner.
>
> This requires then to put both the cancellation state and type on
> a shared state (cancelhandling), since 'pthread_cancel' checks
> whether cancellation is enabled and asynchrnous to either cancel
> itself of sending the signal.
>
> It also requires handle the CANCELING_BITMASK on
> __pthread_disable_asynccancel, however this is incurs in the same

typo: “this is incurs”

> issues described on BZ#12683: the cancellation is acting even *after*

“is acted upon even *after*”?

> the syscalls returns with user visible side-effects.
>
> This patch removes this optimization and simplifies the pthread
> cancellation implementation: pthread_cancel now first check if

typo: check → checks

> cancellation is already pending and if not always send a signal

typo: send → sends

Maybe add a comma before “always”.

> if the target is not itself.  The SIGCANCEL handler is also simpified
> since there is not need to setup a CAS loop.
>
> It also alows to move both the cancellation state and mode out of
> 'cancelhadling' (it is done in subsequent patches).

typo: alows

> diff --git a/nptl/pthread_cancel.c b/nptl/pthread_cancel.c
> index deb404600c..8dfbcff8c3 100644
> --- a/nptl/pthread_cancel.c
> +++ b/nptl/pthread_cancel.c

> @@ -104,72 +87,33 @@ __pthread_cancel (pthread_t th)
>  		    " must be installed for pthread_cancel to work\n");
>    }
> +
> +  int oldch = atomic_fetch_or_acquire (&pd->cancelhandling, CANCELED_BITMASK);
> +  if ((oldch & CANCELED_BITMASK) != 0)
> +    return 0;
> +
> +  if (pd == THREAD_SELF)
>      {
> +      /* A single-threaded process should be able to kill itself, since there
> +	 is nothing in the POSIX specification that says that it cannot.  So
> +	 we set multiple_threads to true so that cancellation points get
> +	 executed.  */
> +      THREAD_SETMEM (THREAD_SELF, header.multiple_threads, 1);
>  #ifndef TLS_MULTIPLE_THREADS_IN_TCB
> -	__libc_multiple_threads = 1;
> +      __libc_multiple_threads = 1;
>  #endif
> +
> +      THREAD_SETMEM (pd, result, PTHREAD_CANCELED);
> +      if ((oldch & CANCELTYPE_BITMASK) != 0)
> +	__do_cancel ();
> +      return 0;
>      }

The last part is for asynchronous self-cancel, right?  Don't we have to
check that cancellation is enabled, too?

Thanks,
Florian


  reply	other threads:[~2021-06-01  9:03 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
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 [this message]
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

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=87bl8q6jok.fsf@oldenburg.str.redhat.com \
    --to=fweimer@redhat.com \
    --cc=libc-alpha@sourceware.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).