Remove cached PID/TID in clone

This patch remove the PID cache and usage in current GLIBC code.  Current
usage is mainly used a performance optimization to avoid the syscall,
however it adds some issues:

  - The exposed clone syscall will try to set pid/tid to make the new
    thread somewhat compatible with current GLIBC assumptions.  This cause
    a set of issue with new workloads and usecases (such as BZ#17214 and
    [1]) as well for new internal usage of clone to optimize other algorithms
    (such as clone plus CLONE_VM for posix_spawn, BZ#19957).

  - The caching complexity also added some bugs in the past [2] [3] and
    requires more effort of each port to handle such requirements (for
    both clone and vfork implementation).

  - Caching performance gain in mainly on getpid and some specific
    code paths.  The getpid performance leverage is questionable [4],
    either by the idea of getpid being a hotspot as for the getpid
    implementation itself (if it is indeed a justifiable hotspot a
    vDSO symbol could let to a much more simpler solution).

    Other usage is mainly for non usual code paths, such as pthread
    cancellation signal and handling.

For thread creation (on stack allocation) the code simplification in fact
adds some performance gain due the no need of transverse the stack cache
and invalidate each element pid.

Other thread usages will require a direct getpid syscall, such as
cancellation/setxid signal, thread cancellation, thread fail path (at
create_thread), and thread signal (pthread_kill and pthread_sigqueue).
However these are hardly usual hotspots and I think adding a syscall is
justifiable.

It also simplifies both the clone and vfork arch-specific implementation.
And by review each fork implementation there are some discrepancies that
this patch also solves:

  - microblaze clone/vfork does not set/reset the pid/tid field
  - hppa uses the default vfork implementation that fallback to fork.
    Since vfork is deprecated I do not think we should bother with it.

The patch also removes the TID caching in clone. My understanding for
such semantic is try provide some pthread usage after a user program
issue clone directly (as done by thread creation with CLONE_PARENT_SETTID
and pthread tid member).  However, as stated before in multiple discussions
threads, GLIBC provides clone syscalls without further supporting all this
semantics.

I ran a full make check on x86_64, x32, i686, armhf, aarch64, and powerpc64le.
For sparc32, sparc64, and mips I ran the basic fork and vfork tests from
posix/ folder (on a qemu system).  So it would require further testing
on alpha, hppa, ia64, m68k, nios2, s390, sh, and tile (I excluded microblaze
because it is already implementing the patch semantic regarding clone/vfork).

[1] https://codereview.chromium.org/800183004/
[2] https://sourceware.org/ml/libc-alpha/2006-07/msg00123.html
[3] https://sourceware.org/bugzilla/show_bug.cgi?id=15368
[4] http://yarchive.net/comp/linux/getpid_caching.html

	* sysdeps/nptl/fork.c (__libc_fork): Remove pid cache setting.
	* nptl/allocatestack.c (allocate_stack): Likewise.
	(__reclaim_stacks): Likewise.
	(setxid_signal_thread): Obtain pid through syscall.
	* nptl/nptl-init.c (sigcancel_handler): Likewise.
	(sighandle_setxid): Likewise.
	* nptl/pthread_cancel.c (pthread_cancel): Likewise.
	* sysdeps/unix/sysv/linux/pthread_kill.c (__pthread_kill): Likewise.
	* sysdeps/unix/sysv/linux/pthread_sigqueue.c (pthread_sigqueue):
	Likewise.
	* sysdeps/unix/sysv/linux/createthread.c (create_thread): Likewise.
	* sysdeps/unix/sysv/linux/getpid.c: Remove file.
	* nptl/descr.h (struct pthread): Change comment about pid value.
	* nptl/pthread_getattr_np.c (pthread_getattr_np): Remove thread
	pid assert.
	* sysdeps/unix/sysv/linux/pthread-pids.h (__pthread_initialize_pids):
	Do not set pid value.
	* nptl_db/td_ta_thr_iter.c (iterate_thread_list): Remove thread
	pid cache check.
	* nptl_db/td_thr_validate.c (td_thr_validate): Likewise.
	* sysdeps/aarch64/nptl/tcb-offsets.sym: Remove pid offset.
	* sysdeps/alpha/nptl/tcb-offsets.sym: Likewise.
	* sysdeps/arm/nptl/tcb-offsets.sym: Likewise.
	* sysdeps/hppa/nptl/tcb-offsets.sym: Likewise.
	* sysdeps/i386/nptl/tcb-offsets.sym: Likewise.
	* sysdeps/ia64/nptl/tcb-offsets.sym: Likewise.
	* sysdeps/m68k/nptl/tcb-offsets.sym: Likewise.
	* sysdeps/microblaze/nptl/tcb-offsets.sym: Likewise.
	* sysdeps/mips/nptl/tcb-offsets.sym: Likewise.
	* sysdeps/nios2/nptl/tcb-offsets.sym: Likewise.
	* sysdeps/powerpc/nptl/tcb-offsets.sym: Likewise.
	* sysdeps/s390/nptl/tcb-offsets.sym: Likewise.
	* sysdeps/sh/nptl/tcb-offsets.sym: Likewise.
	* sysdeps/sparc/nptl/tcb-offsets.sym: Likewise.
	* sysdeps/tile/nptl/tcb-offsets.sym: Likewise.
	* sysdeps/x86_64/nptl/tcb-offsets.sym: Likewise.
	* sysdeps/unix/sysv/linux/aarch64/clone.S: Remove pid and tid caching.
	* sysdeps/unix/sysv/linux/alpha/clone.S: Likewise.
	* sysdeps/unix/sysv/linux/arm/clone.S: Likewise.
	* sysdeps/unix/sysv/linux/hppa/clone.S: Likewise.
	* sysdeps/unix/sysv/linux/i386/clone.S: Likewise.
	* sysdeps/unix/sysv/linux/ia64/clone2.S: Likewise.
	* sysdeps/unix/sysv/linux/mips/clone.S: Likewise.
	* sysdeps/unix/sysv/linux/nios2/clone.S: Likewise.
	* sysdeps/unix/sysv/linux/powerpc/powerpc32/clone.S: Likewise.
	* sysdeps/unix/sysv/linux/powerpc/powerpc64/clone.S: Likewise.
	* sysdeps/unix/sysv/linux/s390/s390-32/clone.S: Likewise.
	* sysdeps/unix/sysv/linux/s390/s390-64/clone.S: Likewise.
	* sysdeps/unix/sysv/linux/sh/clone.S: Likewise.
	* sysdeps/unix/sysv/linux/sparc/sparc32/clone.S: Likewise.
	* sysdeps/unix/sysv/linux/sparc/sparc64/clone.S: Likewise.
	* sysdeps/unix/sysv/linux/tile/clone.S: Likewise.
	* sysdeps/unix/sysv/linux/x86_64/clone.S: Likewise.
	* sysdeps/unix/sysv/linux/aarch64/vfork.S: Remove pid set and reset.
	* sysdeps/unix/sysv/linux/alpha/vfork.S: Likewise.
	* sysdeps/unix/sysv/linux/arm/vfork.S: Likewise.
	* sysdeps/unix/sysv/linux/i386/vfork.S: Likewise.
	* sysdeps/unix/sysv/linux/ia64/vfork.S: Likewise.
	* sysdeps/unix/sysv/linux/m68k/clone.S: Likewise.
	* sysdeps/unix/sysv/linux/m68k/vfork.S: Likewise.
	* sysdeps/unix/sysv/linux/mips/vfork.S: Likewise.
	* sysdeps/unix/sysv/linux/nios2/vfork.S: Likewise.
	* sysdeps/unix/sysv/linux/powerpc/powerpc32/vfork.S: Likewise.
	* sysdeps/unix/sysv/linux/powerpc/powerpc64/vfork.S: Likewise.
	* sysdeps/unix/sysv/linux/s390/s390-32/vfork.S: Likewise.
	* sysdeps/unix/sysv/linux/s390/s390-64/vfork.S: Likewise.
	* sysdeps/unix/sysv/linux/sh/vfork.S: Likewise.
	* sysdeps/unix/sysv/linux/sparc/sparc32/vfork.S: Likewise.
	* sysdeps/unix/sysv/linux/sparc/sparc64/vfork.S: Likewise.
	* sysdeps/unix/sysv/linux/tile/vfork.S: Likewise.
	* sysdeps/unix/sysv/linux/x86_64/vfork.S: Likewise.
	* sysdeps/unix/sysv/linux/tst-clone2.c (f): Remove direct pthread
	struct access.
	(clone_test): Remove function.
	(do_test): Rewrite to take in consideration pid is not cached anymore.

3 files changed, 18 insertions, 62 deletions

diff --git a/nptl_db/structs.def b/nptl_db/structs.def
index a9b621b126..1cb6a46391 100644
--- a/nptl_db/structs.def
+++ b/nptl_db/structs.def
@@ -48,7 +48,6 @@ DB_STRUCT (pthread)
 DB_STRUCT_FIELD (pthread, list)
 DB_STRUCT_FIELD (pthread, report_events)
 DB_STRUCT_FIELD (pthread, tid)
-DB_STRUCT_FIELD (pthread, pid)
 DB_STRUCT_FIELD (pthread, start_routine)
 DB_STRUCT_FIELD (pthread, cancelhandling)
 DB_STRUCT_FIELD (pthread, schedpolicy)
diff --git a/nptl_db/td_ta_thr_iter.c b/nptl_db/td_ta_thr_iter.c
index a990fed150..9e5059956b 100644
--- a/nptl_db/td_ta_thr_iter.c
+++ b/nptl_db/td_ta_thr_iter.c
@@ -76,48 +76,28 @@ iterate_thread_list (td_thragent_t *ta, td_thr_iter_f *callback,
       if (ps_pdread (ta->ph, addr, copy, ta->ta_sizeof_pthread) != PS_OK)
 	return TD_ERR;
 
-      /* Verify that this thread's pid field matches the child PID.
-	 If its pid field is negative, it's about to do a fork or it
-	 is the sole thread in a fork child.  */
-      psaddr_t pid;
-      err = DB_GET_FIELD_LOCAL (pid, ta, copy, pthread, pid, 0);
-      if (err == TD_OK && (pid_t) (uintptr_t) pid < 0)
-	{
-	  if (-(pid_t) (uintptr_t) pid == match_pid)
-	    /* It is about to do a fork, but is really still the parent PID.  */
-	    pid = (psaddr_t) (uintptr_t) match_pid;
-	  else
-	    /* It must be a fork child, whose new PID is in the tid field.  */
-	    err = DB_GET_FIELD_LOCAL (pid, ta, copy, pthread, tid, 0);
-	}
+      err = DB_GET_FIELD_LOCAL (schedpolicy, ta, copy, pthread,
+				schedpolicy, 0);
       if (err != TD_OK)
 	break;
+      err = DB_GET_FIELD_LOCAL (schedprio, ta, copy, pthread,
+				schedparam_sched_priority, 0);
+      if (err != TD_OK)
+	break;
+
+      /* Now test whether this thread matches the specified conditions.  */
 
-      if ((pid_t) (uintptr_t) pid == match_pid)
+      /* Only if the priority level is as high or higher.  */
+      int descr_pri = ((uintptr_t) schedpolicy == SCHED_OTHER
+		       ? 0 : (uintptr_t) schedprio);
+      if (descr_pri >= ti_pri)
 	{
-	  err = DB_GET_FIELD_LOCAL (schedpolicy, ta, copy, pthread,
-				    schedpolicy, 0);
-	  if (err != TD_OK)
-	    break;
-	  err = DB_GET_FIELD_LOCAL (schedprio, ta, copy, pthread,
-				    schedparam_sched_priority, 0);
-	  if (err != TD_OK)
-	    break;
-
-	  /* Now test whether this thread matches the specified conditions.  */
-
-	  /* Only if the priority level is as high or higher.  */
-	  int descr_pri = ((uintptr_t) schedpolicy == SCHED_OTHER
-			   ? 0 : (uintptr_t) schedprio);
-	  if (descr_pri >= ti_pri)
-	    {
-	      /* Yep, it matches.  Call the callback function.  */
-	      td_thrhandle_t th;
-	      th.th_ta_p = (td_thragent_t *) ta;
-	      th.th_unique = addr;
-	      if (callback (&th, cbdata_p) != 0)
-		return TD_DBERR;
-	    }
+	  /* Yep, it matches.  Call the callback function.  */
+	  td_thrhandle_t th;
+	  th.th_ta_p = (td_thragent_t *) ta;
+	  th.th_unique = addr;
+	  if (callback (&th, cbdata_p) != 0)
+	    return TD_DBERR;
 	}
 
       /* Get the pointer to the next element.  */
diff --git a/nptl_db/td_thr_validate.c b/nptl_db/td_thr_validate.c
index f3c8a7bed6..9b89fecad2 100644
--- a/nptl_db/td_thr_validate.c
+++ b/nptl_db/td_thr_validate.c
@@ -80,28 +80,5 @@ td_thr_validate (const td_thrhandle_t *th)
 	err = TD_OK;
     }
 
-  if (err == TD_OK)
-    {
-      /* Verify that this is not a stale element in a fork child.  */
-      pid_t match_pid = ps_getpid (th->th_ta_p->ph);
-      psaddr_t pid;
-      err = DB_GET_FIELD (pid, th->th_ta_p, th->th_unique, pthread, pid, 0);
-      if (err == TD_OK && (pid_t) (uintptr_t) pid < 0)
-	{
-	  /* This was a thread that was about to fork, or it is the new sole
-	     thread in a fork child.  In the latter case, its tid was stored
-	     via CLONE_CHILD_SETTID and so is already the proper child PID.  */
-	  if (-(pid_t) (uintptr_t) pid == match_pid)
-	    /* It is about to do a fork, but is really still the parent PID.  */
-	    pid = (psaddr_t) (uintptr_t) match_pid;
-	  else
-	    /* It must be a fork child, whose new PID is in the tid field.  */
-	    err = DB_GET_FIELD (pid, th->th_ta_p, th->th_unique,
-				pthread, tid, 0);
-	}
-      if (err == TD_OK && (pid_t) (uintptr_t) pid != match_pid)
-	err = TD_NOTHR;
-    }
-
   return err;
 }