Patchwork Refactor Linux raise implementation (BZ#15368)

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Submitter Adhemerval Zanella Netto
Date June 18, 2016, 5:25 p.m.
Message ID <57658427.2090902@linaro.org>
Download mbox | patch
Permalink /patch/13220/
State Under Review
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Comments

Adhemerval Zanella Netto - June 18, 2016, 5:25 p.m.
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.

--
Adhemerval Zanella Netto - June 29, 2016, 12:57 p.m.
Ping.

On 18/06/2016 14:25, Adhemerval Zanella wrote:
> 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)
>
Adhemerval Zanella Netto - July 7, 2016, 3:16 p.m.
Ping x2 (I would like to push it before hard freeze).

On 29/06/2016 09:57, Adhemerval Zanella wrote:
> Ping.
> 
> On 18/06/2016 14:25, Adhemerval Zanella wrote:
>> 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)
>>
Andreas Schwab - July 7, 2016, 3:30 p.m.
Adhemerval Zanella <adhemerval.zanella@linaro.org> writes:

> +  /* 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.  */

s/issues/issue/; s/^/ syscalls/

> +  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);

What if block/unblock fail?

Andreas.
Adhemerval Zanella Netto - July 7, 2016, 4:12 p.m.
On 07/07/2016 12:30, Andreas Schwab wrote:
> Adhemerval Zanella <adhemerval.zanella@linaro.org> writes:
> 
>> +  /* 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.  */
> 
> s/issues/issue/; s/^/ syscalls/

Right, I will fix it.

> 
>> +  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);
> 
> What if block/unblock fail?

My understanding checking on kernel source is 'rt_sigprocmask' may fail if:

  1. sigsetsize != sizeof (sigset_t) (EINVAL)
  2. a failure in copy_from_user/copy_to_user (EFAULT)
  3. an invalid 'how' operation (EINVAL)

The first case is already handle in glibc syscall call by using the arch 
defined _NSIG.  Second is handled by using a stack allocated mask in 'raise'
implementation.  The last one should be handled by the
__libc_signal_{un}block_{app,all} macros.

I think there is no need in this specific usage to handle failures.
Andreas Schwab - July 11, 2016, 7:07 a.m.
Adhemerval Zanella <adhemerval.zanella@linaro.org> writes:

> I think there is no need in this specific usage to handle failures.

Could you please add a comment to that effect?

Andreas.
Adhemerval Zanella Netto - July 11, 2016, 8:05 a.m.
On 11/07/2016 04:07, Andreas Schwab wrote:
> Adhemerval Zanella <adhemerval.zanella@linaro.org> writes:
> 
>> I think there is no need in this specific usage to handle failures.
> 
> Could you please add a comment to that effect?
> 
> Andreas.
> 

I will do it.

Patch

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)