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Fix change to prevent cancel signal in unsafe places.

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The bits tested to decide when to delay the return when switching
off async cancel mode were wrong.  Fix that.  Also close a race
condition in pthread_cancel where the bit indicating the cancellation
is unconditionally set even if the cancel type might have changed.
This commit is contained in:
Ulrich Drepper
2009-05-15 20:42:36 -07:00
parent bbc5d74dd0
commit 9437b427ce
4 changed files with 16 additions and 14 deletions
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6
nptl/ChangeLog
View File

@ -1,5 +1,11 @@
2009-05-15 Ulrich Drepper <drepper@redhat.com> 2009-05-15 Ulrich Drepper <drepper@redhat.com>
* cancellation.c (__pthread_disable_asynccancel): Correct the bits
to test when deciding on the delay.
* libc-cancellation.c (__libc_disable_asynccancel): Likewise.
* pthread_cancel.c: Close race between deciding on sending a signal
and setting the CANCELING_BIT bit.
* cancellation.c (__pthread_disable_asynccancel): Don't return if * cancellation.c (__pthread_disable_asynccancel): Don't return if
thread is canceled. thread is canceled.
* libc-cancellation.c (__libc_disable_asynccancel): Likewise. * libc-cancellation.c (__libc_disable_asynccancel): Likewise.

8
nptl/cancellation.c
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@ -72,10 +72,6 @@ __pthread_disable_asynccancel (int oldtype)
struct pthread *self = THREAD_SELF; struct pthread *self = THREAD_SELF;
int newval; int newval;
#ifdef THREAD_ATOMIC_AND
THREAD_ATOMIC_AND (self, cancelhandling, ~CANCELTYPE_BITMASK);
newval = THREAD_GETMEM (self, cancelhandling);
#else
int oldval = THREAD_GETMEM (self, cancelhandling); int oldval = THREAD_GETMEM (self, cancelhandling);
while (1) while (1)
@ -93,13 +89,13 @@ __pthread_disable_asynccancel (int oldtype)
/* Prepare the next round. */ /* Prepare the next round. */
oldval = curval; oldval = curval;
} }
#endif
/* We cannot return when we are being canceled. Upon return the /* We cannot return when we are being canceled. Upon return the
thread might be things which would have to be undone. The thread might be things which would have to be undone. The
following loop should loop until the cancellation signal is following loop should loop until the cancellation signal is
delivered. */ delivered. */
while (__builtin_expect (newval & CANCELED_BITMASK, 0)) while (__builtin_expect ((newval & (CANCELING_BITMASK | CANCELED_BITMASK))
== CANCELING_BITMASK, 0))
{ {
lll_futex_wait (&self->cancelhandling, newval, LLL_PRIVATE); lll_futex_wait (&self->cancelhandling, newval, LLL_PRIVATE);
newval = THREAD_GETMEM (self, cancelhandling); newval = THREAD_GETMEM (self, cancelhandling);

8
nptl/libc-cancellation.c
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@ -88,10 +88,6 @@ __libc_disable_asynccancel (int oldtype)
struct pthread *self = THREAD_SELF; struct pthread *self = THREAD_SELF;
int newval; int newval;
#ifdef THREAD_ATOMIC_AND
THREAD_ATOMIC_AND (self, cancelhandling, ~CANCELTYPE_BITMASK);
newval = THREAD_GETMEM (self, cancelhandling);
#else
int oldval = THREAD_GETMEM (self, cancelhandling); int oldval = THREAD_GETMEM (self, cancelhandling);
while (1) while (1)
@ -109,13 +105,13 @@ __libc_disable_asynccancel (int oldtype)
/* Prepare the next round. */ /* Prepare the next round. */
oldval = curval; oldval = curval;
} }
#endif
/* We cannot return when we are being canceled. Upon return the /* We cannot return when we are being canceled. Upon return the
thread might be things which would have to be undone. The thread might be things which would have to be undone. The
following loop should loop until the cancellation signal is following loop should loop until the cancellation signal is
delivered. */ delivered. */
while (__builtin_expect (newval & CANCELED_BITMASK, 0)) while (__builtin_expect ((newval & (CANCELING_BITMASK | CANCELED_BITMASK))
== CANCELING_BITMASK, 0))
{ {
lll_futex_wait (&self->cancelhandling, newval, LLL_PRIVATE); lll_futex_wait (&self->cancelhandling, newval, LLL_PRIVATE);
newval = THREAD_GETMEM (self, cancelhandling); newval = THREAD_GETMEM (self, cancelhandling);

8
nptl/pthread_cancel.c
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@ -1,4 +1,4 @@
/* Copyright (C) 2002, 2003, 2004 Free Software Foundation, Inc. /* Copyright (C) 2002, 2003, 2004, 2009 Free Software Foundation, Inc.
This file is part of the GNU C Library. This file is part of the GNU C Library.
Contributed by Ulrich Drepper <drepper@redhat.com>, 2002. Contributed by Ulrich Drepper <drepper@redhat.com>, 2002.
@ -44,6 +44,7 @@ pthread_cancel (th)
int newval; int newval;
do do
{ {
again:
oldval = pd->cancelhandling; oldval = pd->cancelhandling;
newval = oldval | CANCELING_BITMASK | CANCELED_BITMASK; newval = oldval | CANCELING_BITMASK | CANCELED_BITMASK;
@ -59,7 +60,10 @@ pthread_cancel (th)
if (CANCEL_ENABLED_AND_CANCELED_AND_ASYNCHRONOUS (newval)) if (CANCEL_ENABLED_AND_CANCELED_AND_ASYNCHRONOUS (newval))
{ {
/* Mark the cancellation as "in progress". */ /* Mark the cancellation as "in progress". */
atomic_bit_set (&pd->cancelhandling, CANCELING_BIT); if (atomic_compare_and_exchange_bool_acq (&pd->cancelhandling,
oldval | CANCELING_BITMASK,
oldval))
goto again;
/* The cancellation handler will take care of marking the /* The cancellation handler will take care of marking the
thread as canceled. */ thread as canceled. */