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Re: [PATCH] Refactor Linux raise implementation (BZ#15368)
- From: Adhemerval Zanella <adhemerval dot zanella at linaro dot org>
- To: Zack Weinberg <zackw at panix dot com>
- Cc: GNU C Library <libc-alpha at sourceware dot org>
- Date: Sat, 18 Jun 2016 14:25:59 -0300
- Subject: Re: [PATCH] Refactor Linux raise implementation (BZ#15368)
- Authentication-results: sourceware.org; auth=none
- References: <1466188988-19954-1-git-send-email-adhemerval dot zanella at linaro dot org> <CAKCAbMgJvz1QagpX8kAtCjEgJE8D0SPABvcJ6VFZ-Vt+cDMTNA at mail dot gmail dot com>
Thanks for reviews, comment below:
On 18/06/2016 11:09, Zack Weinberg wrote:
> On Fri, Jun 17, 2016 at 2:43 PM, Adhemerval Zanella
> <adhemerval.zanella@linaro.org> wrote:
>> This patch changes both the nptl and libc Linux raise implementation
>> to avoid the issues described in BZ#15368.
>
> It would be nice to have comments in these files which explain why it
> is necessary to block all signals and why the cached values are not
> safe to use. The old comment that you deleted ("raise is async-safe
> and could be called while fork/vfork temporarily invalidated the PID")
> would be a good start.
>
Indeed, I did not remove them in this new version below. I also extended
the comment a bit explaining why to block the application signals.
>> The strategy used is
>> summarized in bug report first comment:
>>
>> 1. Block all signals (including internal NPTL ones);
>
> The code appears to block all signals *except* the internal NPTL ones.
> If I understand Rich's description of the problem correctly, that is
> wrong.
Right, we need to block only user defined handler that might fork/vfork.
The call itself is OK, but I will change the comments describing why there
is no need to block GLIBC internal handlers.
>
>> +static inline int
>> +__libc_signal_block_all (const sigset_t *set)
>> +{
>
> Type-safety error here: the 'set' argument is written to and should
> not be 'const'. It compiles because INTERNAL_SYSCALL() erases types,
> but the compiler would be entitled to assume that 'set' is unchanged
> after the call.
Ack.
>
>> +static inline int
>> +__libc_signal_block_app (const sigset_t *set)
>
> Same type-safety error here.
Ack.
>
>> + sigset_t set;
>> + __libc_signal_block_app (&set);
>> +
>> + pid_t pid = __getpid ();
>
> If I'm reading the code correctly, __getpid does *not* bypass the cache.
>
>> + pid_t tid = INLINE_SYSCALL (gettid, 0);
>
> INTERNAL_SYSCALL() here too? gettid() can't fail, so there's no point
> generating the code to potentially set errno.
>
Right, I will use INTERNAL_SYSCALL.
> zw
>
I think this version addresses all the issues you raised:
--
* sysdeps/unix/sysv/linux/nptl-signals.h
(__nptl_clear_internal_signals): New function.
(__libc_signal_block_all): Likewise.
(__libc_signal_block_app): Likewise.
(__libc_signal_restore_set): Likewise.
* sysdeps/unix/sysv/linux/pt-raise.c (raise): Use Linux raise.c
implementation.
* sysdeps/unix/sysv/linux/raise.c (raise): Reimplement to not use
the cached pid/tid value in pthread structure.
--
diff --git a/sysdeps/unix/sysv/linux/nptl-signals.h b/sysdeps/unix/sysv/linux/nptl-signals.h
index 01f34c2..6525b6d 100644
--- a/sysdeps/unix/sysv/linux/nptl-signals.h
+++ b/sysdeps/unix/sysv/linux/nptl-signals.h
@@ -39,5 +39,42 @@ __nptl_is_internal_signal (int sig)
return (sig == SIGCANCEL) || (sig == SIGTIMER) || (sig == SIGSETXID);
}
+static inline void
+__nptl_clear_internal_signals (sigset_t *set)
+{
+ __sigdelset (set, SIGCANCEL);
+ __sigdelset (set, SIGTIMER);
+ __sigdelset (set, SIGSETXID);
+}
+
+#define SIGALL_SET \
+ ((__sigset_t) { .__val = {[0 ... _SIGSET_NWORDS-1 ] = -1 } })
+
+static inline int
+__libc_signal_block_all (sigset_t *set)
+{
+ INTERNAL_SYSCALL_DECL (err);
+ return INTERNAL_SYSCALL (rt_sigprocmask, err, 4, SIG_BLOCK, &SIGALL_SET,
+ set, _NSIG / 8);
+}
+
+static inline int
+__libc_signal_block_app (sigset_t *set)
+{
+ sigset_t allset = SIGALL_SET;
+ __nptl_clear_internal_signals (&allset);
+ INTERNAL_SYSCALL_DECL (err);
+ return INTERNAL_SYSCALL (rt_sigprocmask, err, 4, SIG_BLOCK, &allset, set,
+ _NSIG / 8);
+}
+
+static inline int
+__libc_signal_restore_set (const sigset_t *set)
+{
+ INTERNAL_SYSCALL_DECL (err);
+ return INTERNAL_SYSCALL (rt_sigprocmask, err, 4, SIG_SETMASK, set, NULL,
+ _NSIG / 8);
+}
+
/* Used to communicate with signal handler. */
extern struct xid_command *__xidcmd attribute_hidden;
diff --git a/sysdeps/unix/sysv/linux/pt-raise.c b/sysdeps/unix/sysv/linux/pt-raise.c
index 715bbe9..5f6dea1 100644
--- a/sysdeps/unix/sysv/linux/pt-raise.c
+++ b/sysdeps/unix/sysv/linux/pt-raise.c
@@ -1,4 +1,5 @@
-/* Copyright (C) 2002-2016 Free Software Foundation, Inc.
+/* ISO C raise function for libpthread.
+ Copyright (C) 2002-2016 Free Software Foundation, Inc.
This file is part of the GNU C Library.
Contributed by Ulrich Drepper <drepper@redhat.com>, 2002.
@@ -16,22 +17,4 @@
License along with the GNU C Library; if not, see
<http://www.gnu.org/licenses/>. */
-#include <errno.h>
-#include <signal.h>
-#include <sysdep.h>
-#include <tls.h>
-
-
-int
-raise (int sig)
-{
- /* raise is an async-safe function. It could be called while the
- fork function temporarily invalidated the PID field. Adjust for
- that. */
- pid_t pid = THREAD_GETMEM (THREAD_SELF, pid);
- if (__glibc_unlikely (pid < 0))
- pid = -pid;
-
- return INLINE_SYSCALL (tgkill, 3, pid, THREAD_GETMEM (THREAD_SELF, tid),
- sig);
-}
+#include <sysdeps/unix/sysv/linux/raise.c>
diff --git a/sysdeps/unix/sysv/linux/raise.c b/sysdeps/unix/sysv/linux/raise.c
index 3795e6e..d386426 100644
--- a/sysdeps/unix/sysv/linux/raise.c
+++ b/sysdeps/unix/sysv/linux/raise.c
@@ -16,42 +16,34 @@
License along with the GNU C Library; if not, see
<http://www.gnu.org/licenses/>. */
-#include <errno.h>
-#include <limits.h>
#include <signal.h>
#include <sysdep.h>
-#include <nptl/pthreadP.h>
-
+#include <errno.h>
+#include <sys/types.h>
+#include <unistd.h>
+#include <nptl-signals.h>
int
raise (int sig)
{
- struct pthread *pd = THREAD_SELF;
- pid_t pid = THREAD_GETMEM (pd, pid);
- pid_t selftid = THREAD_GETMEM (pd, tid);
- if (selftid == 0)
- {
- /* This system call is not supposed to fail. */
-#ifdef INTERNAL_SYSCALL
- INTERNAL_SYSCALL_DECL (err);
- selftid = INTERNAL_SYSCALL (gettid, err, 0);
-#else
- selftid = INLINE_SYSCALL (gettid, 0);
-#endif
- THREAD_SETMEM (pd, tid, selftid);
-
- /* We do not set the PID field in the TID here since we might be
- called from a signal handler while the thread executes fork. */
- pid = selftid;
- }
- else
- /* raise is an async-safe function. It could be called while the
- fork/vfork function temporarily invalidated the PID field. Adjust for
- that. */
- if (__glibc_unlikely (pid <= 0))
- pid = (pid & INT_MAX) == 0 ? selftid : -pid;
-
- return INLINE_SYSCALL (tgkill, 3, pid, selftid, sig);
+ /* raise is an async-safe function so it could be called while the
+ fork/vfork function temporarily invalidated the PID field. To avoid
+ relying in the cached value we block all user-defined signal handler
+ (which might call fork/vfork) and issues the getpid and gettid
+ directly. */
+
+ sigset_t set;
+ __libc_signal_block_app (&set);
+
+ INTERNAL_SYSCALL_DECL (err);
+ pid_t pid = INTERNAL_SYSCALL (getpid, err, 0);
+ pid_t tid = INTERNAL_SYSCALL (gettid, err, 0);
+
+ int ret = INLINE_SYSCALL (tgkill, 3, pid, tid, sig);
+
+ __libc_signal_restore_set (&set);
+
+ return ret;
}
libc_hidden_def (raise)
weak_alias (raise, gsignal)