[06/11] nptl: Install cancellation handler on pthread_cancel
Checks
Commit Message
Now that cancellation is not used anymore to handle thread setup
creation failure, the sighandle can be installed only when
pthread_cancel is actually used.
Checked on x86_64-linux-gnu and aarch64-linux-gnu.
---
nptl/Versions | 3 +--
nptl/pthreadP.h | 6 ------
nptl/pthread_cancel.c | 49 ++++++++++++++++++++++++-------------------
nptl/pthread_create.c | 15 -------------
4 files changed, 28 insertions(+), 45 deletions(-)
Comments
* Adhemerval Zanella via Libc-alpha:
> @@ -134,7 +135,11 @@ __pthread_cancel (pthread_t th)
> call pthread_cancel (pthread_self ()) without calling
> pthread_create, so the signal handler may not have been
> set up for a self-cancel. */
> - sigcancel_handler ();
> + {
> + THREAD_SETMEM (pd, result, PTHREAD_CANCELED);
> + if ((newval & CANCELTYPE_BITMASK) != 0)
> + __do_cancel ();
> + }
The comment is no longer up to date, I think. Rest of the change looks
okay to me.
Thanks,
Florian
On 26/05/2021 14:38, Florian Weimer wrote:
> * Adhemerval Zanella via Libc-alpha:
>
>> @@ -134,7 +135,11 @@ __pthread_cancel (pthread_t th)
>> call pthread_cancel (pthread_self ()) without calling
>> pthread_create, so the signal handler may not have been
>> set up for a self-cancel. */
>> - sigcancel_handler ();
>> + {
>> + THREAD_SETMEM (pd, result, PTHREAD_CANCELED);
>> + if ((newval & CANCELTYPE_BITMASK) != 0)
>> + __do_cancel ();
>> + }
>
> The comment is no longer up to date, I think. Rest of the change looks
> okay to me.
Indeed, I will remove it.
@@ -395,7 +395,6 @@ libc {
__nptl_free_tcb;
__nptl_nthreads;
__nptl_setxid_sighandler;
- __nptl_sigcancel_handler;
__nptl_stack_list_add;
__nptl_stack_list_del;
__pthread_attr_copy;
@@ -514,4 +513,4 @@ ld {
__nptl_initial_report_events;
__nptl_set_robust_list_avail;
}
-}
\ No newline at end of file
+}
@@ -569,12 +569,6 @@ libc_hidden_proto (__pthread_attr_setsigmask_internal)
extern __typeof (pthread_attr_getsigmask_np) __pthread_attr_getsigmask_np;
libc_hidden_proto (__pthread_attr_getsigmask_np)
-/* The cancellation signal handler defined alongside with
- pthread_cancel. This is included in statically linked binaries
- only if pthread_cancel is linked in. */
-void __nptl_sigcancel_handler (int sig, siginfo_t *si, void *ctx);
-libc_hidden_proto (__nptl_sigcancel_handler)
-
/* Special versions which use non-exported functions. */
extern void __pthread_cleanup_push (struct _pthread_cleanup_buffer *buffer,
void (*routine) (void *), void *arg);
@@ -28,11 +28,19 @@
#include <gnu/lib-names.h>
#include <sys/single_threaded.h>
-/* For asynchronous cancellation we use a signal. This is the core
- logic of the signal handler. */
+/* For asynchronous cancellation we use a signal. */
static void
-sigcancel_handler (void)
+sigcancel_handler (int sig, siginfo_t *si, void *ctx)
{
+ /* Safety check. It would be possible to call this function for
+ other signals and send a signal from another process. This is not
+ correct and might even be a security problem. Try to catch as
+ many incorrect invocations as possible. */
+ if (sig != SIGCANCEL
+ || si->si_pid != __getpid()
+ || si->si_code != SI_TKILL)
+ return;
+
struct pthread *self = THREAD_SELF;
int oldval = THREAD_GETMEM (self, cancelhandling);
@@ -66,24 +74,6 @@ sigcancel_handler (void)
}
}
-/* This is the actually installed SIGCANCEL handler. It adds some
- safety checks before performing the cancellation. */
-void
-__nptl_sigcancel_handler (int sig, siginfo_t *si, void *ctx)
-{
- /* Safety check. It would be possible to call this function for
- other signals and send a signal from another process. This is not
- correct and might even be a security problem. Try to catch as
- many incorrect invocations as possible. */
- if (sig != SIGCANCEL
- || si->si_pid != __getpid()
- || si->si_code != SI_TKILL)
- return;
-
- sigcancel_handler ();
-}
-libc_hidden_def (__nptl_sigcancel_handler)
-
int
__pthread_cancel (pthread_t th)
{
@@ -94,6 +84,17 @@ __pthread_cancel (pthread_t th)
/* Not a valid thread handle. */
return ESRCH;
+ static int init_sigcancel = 0;
+ if (atomic_load_relaxed (&init_sigcancel) == 0)
+ {
+ struct sigaction sa;
+ sa.sa_sigaction = sigcancel_handler;
+ sa.sa_flags = SA_SIGINFO;
+ __sigemptyset (&sa.sa_mask);
+ __libc_sigaction (SIGCANCEL, &sa, NULL);
+ atomic_store_relaxed (&init_sigcancel, 1);
+ }
+
#ifdef SHARED
/* Trigger an error if libgcc_s cannot be loaded. */
{
@@ -134,7 +135,11 @@ __pthread_cancel (pthread_t th)
call pthread_cancel (pthread_self ()) without calling
pthread_create, so the signal handler may not have been
set up for a self-cancel. */
- sigcancel_handler ();
+ {
+ THREAD_SETMEM (pd, result, PTHREAD_CANCELED);
+ if ((newval & CANCELTYPE_BITMASK) != 0)
+ __do_cancel ();
+ }
else
{
/* The cancellation handler will take care of marking the
@@ -68,21 +68,6 @@ late_init (void)
struct sigaction sa;
__sigemptyset (&sa.sa_mask);
- /* Install the cancellation signal handler (in static builds only if
- pthread_cancel has been linked in). If for some reason we cannot
- install the handler we do not abort. Maybe we should, but it is
- only asynchronous cancellation which is affected. */
-#ifndef SHARED
- extern __typeof (__nptl_sigcancel_handler) __nptl_sigcancel_handler
- __attribute__ ((weak));
- if (__nptl_sigcancel_handler != NULL)
-#endif
- {
- sa.sa_sigaction = __nptl_sigcancel_handler;
- sa.sa_flags = SA_SIGINFO;
- (void) __libc_sigaction (SIGCANCEL, &sa, NULL);
- }
-
/* Install the handle to change the threads' uid/gid. */
sa.sa_sigaction = __nptl_setxid_sighandler;
sa.sa_flags = SA_SIGINFO | SA_RESTART;