glibc/nptl/cancellation.c
Adhemerval Zanella 404656009b nptl: Handle spurious EINTR when thread cancellation is disabled (BZ#29029)
Some Linux interfaces never restart after being interrupted by a signal
handler, regardless of the use of SA_RESTART [1].  It means that for
pthread cancellation, if the target thread disables cancellation with
pthread_setcancelstate and calls such interfaces (like poll or select),
it should not see spurious EINTR failures due the internal SIGCANCEL.

However recent changes made pthread_cancel to always sent the internal
signal, regardless of the target thread cancellation status or type.
To fix it, the previous semantic is restored, where the cancel signal
is only sent if the target thread has cancelation enabled in
asynchronous mode.

The cancel state and cancel type is moved back to cancelhandling
and atomic operation are used to synchronize between threads.  The
patch essentially revert the following commits:

  8c1c0aae20 nptl: Move cancel type out of cancelhandling
  2b51742531 nptl: Move cancel state out of cancelhandling
  26cfbb7162 nptl: Remove CANCELING_BITMASK

However I changed the atomic operation to follow the internal C11
semantic and removed the MACRO usage, it simplifies a bit the
resulting code (and removes another usage of the old atomic macros).

Checked on x86_64-linux-gnu, i686-linux-gnu, aarch64-linux-gnu,
and powerpc64-linux-gnu.

[1] https://man7.org/linux/man-pages/man7/signal.7.html

Reviewed-by: Florian Weimer <fweimer@redhat.com>
Tested-by: Aurelien Jarno <aurelien@aurel32.net>
2022-04-14 12:48:31 -03:00

92 lines
2.8 KiB
C

/* Copyright (C) 2002-2022 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
<https://www.gnu.org/licenses/>. */
#include <setjmp.h>
#include <stdlib.h>
#include "pthreadP.h"
#include <futex-internal.h>
/* The next two functions are similar to pthread_setcanceltype() but
more specialized for the use in the cancelable functions like write().
They do not need to check parameters etc. These functions must be
AS-safe, with the exception of the actual cancellation, because they
are called by wrappers around AS-safe functions like write().*/
int
__pthread_enable_asynccancel (void)
{
struct pthread *self = THREAD_SELF;
int oldval = atomic_load_relaxed (&self->cancelhandling);
while (1)
{
int newval = oldval | CANCELTYPE_BITMASK;
if (newval == oldval)
break;
if (atomic_compare_exchange_weak_acquire (&self->cancelhandling,
&oldval, newval))
{
if (cancel_enabled_and_canceled_and_async (newval))
{
self->result = PTHREAD_CANCELED;
__do_cancel ();
}
break;
}
}
return oldval;
}
libc_hidden_def (__pthread_enable_asynccancel)
/* See the comment for __pthread_enable_asynccancel regarding
the AS-safety of this function. */
void
__pthread_disable_asynccancel (int oldtype)
{
/* If asynchronous cancellation was enabled before we do not have
anything to do. */
if (oldtype & CANCELTYPE_BITMASK)
return;
struct pthread *self = THREAD_SELF;
int newval;
int oldval = atomic_load_relaxed (&self->cancelhandling);
do
{
newval = oldval & ~CANCELTYPE_BITMASK;
}
while (!atomic_compare_exchange_weak_acquire (&self->cancelhandling,
&oldval, newval));
/* We cannot return when we are being canceled. Upon return the
thread might be things which would have to be undone. The
following loop should loop until the cancellation signal is
delivered. */
while (__glibc_unlikely ((newval & (CANCELING_BITMASK | CANCELED_BITMASK))
== CANCELING_BITMASK))
{
futex_wait_simple ((unsigned int *) &self->cancelhandling, newval,
FUTEX_PRIVATE);
newval = atomic_load_relaxed (&self->cancelhandling);
}
}
libc_hidden_def (__pthread_disable_asynccancel)