[PATCH v2 05/19] nptl: Move setxid flag out of cancelhandling

[Adhemerval Zanella]

Now that the thread state is tracked by 'joinstate' field, there is no
need to keep the setxid flag within the 'cancelhandling'.  It simplifies
the atomic code to set and reset it (since there is no need to handle
the thread state concurrent update).

Checked on x86_64-linux-gnu and aarch64-linux-gnu.
---
 nptl/allocatestack.c  |  3 +++
 nptl/descr.h          |  5 ++---
 nptl/nptl_setxid.c    | 49 ++++++++++---------------------------------
 nptl/pthread_create.c |  4 ++--
 4 files changed, 18 insertions(+), 43 deletions(-)

diff --git a/nptl/allocatestack.c b/nptl/allocatestack.c
index cfe37a3443..ccb1aa21c1 100644
--- a/nptl/allocatestack.c
+++ b/nptl/allocatestack.c
@@ -99,6 +99,7 @@ get_cached_stack (size_t *sizep, void **memp)
     }
 
   /* Don't allow setxid until cloned.  */
+  result->setxid_flag = 0;
   result->setxid_futex = -1;
 
   /* Dequeue the entry.  */
@@ -301,6 +302,7 @@ allocate_stack (const struct pthread_attr *attr, struct pthread **pdp,
 #endif
 
       /* Don't allow setxid until cloned.  */
+      pd->setxid_flag = 0;
       pd->setxid_futex = -1;
 
       /* Allocate the DTV for this thread.  */
@@ -422,6 +424,7 @@ allocate_stack (const struct pthread_attr *attr, struct pthread **pdp,
 #endif
 
 	  /* Don't allow setxid until cloned.  */
+	  pd->setxid_flag = 0;
 	  pd->setxid_futex = -1;
 
 	  /* Allocate the DTV for this thread.  */
diff --git a/nptl/descr.h b/nptl/descr.h
index 4b2db6edab..563b152bff 100644
--- a/nptl/descr.h
+++ b/nptl/descr.h
@@ -297,9 +297,6 @@ struct pthread
   /* Bit set if thread terminated and TCB is freed.  */
 #define TERMINATED_BIT		5
 #define TERMINATED_BITMASK	(0x01 << TERMINATED_BIT)
-  /* Bit set if thread is supposed to change XID.  */
-#define SETXID_BIT		6
-#define SETXID_BITMASK		(0x01 << SETXID_BIT)
 
   /* Flags.  Including those copied from the thread attribute.  */
   int flags;
@@ -339,6 +336,8 @@ struct pthread
   /* Lock to synchronize access to the descriptor.  */
   int lock;
 
+  /* Indicate whether thread is supposed to change XID.  */
+  int setxid_flag;
   /* Lock for synchronizing setxid calls.  */
   unsigned int setxid_futex;
 
diff --git a/nptl/nptl_setxid.c b/nptl/nptl_setxid.c
index 2f35772411..c337fa8577 100644
--- a/nptl/nptl_setxid.c
+++ b/nptl/nptl_setxid.c
@@ -76,14 +76,7 @@ __nptl_setxid_sighandler (int sig, siginfo_t *si, void *ctx)
 
   /* Reset the SETXID flag.  */
   struct pthread *self = THREAD_SELF;
-  int flags, newval;
-  do
-    {
-      flags = THREAD_GETMEM (self, cancelhandling);
-      newval = THREAD_ATOMIC_CMPXCHG_VAL (self, cancelhandling,
-					  flags & ~SETXID_BITMASK, flags);
-    }
-  while (flags != newval);
+  atomic_store_release (&self->setxid_flag, 0);
 
   /* And release the futex.  */
   self->setxid_futex = 1;
@@ -97,8 +90,6 @@ libc_hidden_def (__nptl_setxid_sighandler)
 static void
 setxid_mark_thread (struct xid_command *cmdp, struct pthread *t)
 {
-  int ch;
-
   /* Wait until this thread is cloned.  */
   if (t->setxid_futex == -1
       && ! atomic_compare_and_exchange_bool_acq (&t->setxid_futex, -2, -1))
@@ -109,41 +100,23 @@ setxid_mark_thread (struct xid_command *cmdp, struct pthread *t)
   /* Don't let the thread exit before the setxid handler runs.  */
   t->setxid_futex = 0;
 
-  do
-    {
-      ch = t->cancelhandling;
+  /* If thread is exiting right now, ignore it.  */
+  if (atomic_load_acquire (&t->joinstate) == THREAD_STATE_EXITING)
+    return;
 
-      /* If the thread is exiting right now, ignore it.  */
-      if ((ch & EXITING_BITMASK) != 0)
-        {
-          /* Release the futex if there is no other setxid in
-             progress.  */
-          if ((ch & SETXID_BITMASK) == 0)
-            {
-              t->setxid_futex = 1;
-              futex_wake (&t->setxid_futex, 1, FUTEX_PRIVATE);
-            }
-          return;
-        }
+  /* Release the futex if there is no other setxid in progress.  */
+  if (atomic_exchange_acquire (&t->setxid_flag, 1) == 0)
+    {
+      t->setxid_futex = 1;
+      futex_wake (&t->setxid_futex, 1, FUTEX_PRIVATE);
     }
-  while (atomic_compare_and_exchange_bool_acq (&t->cancelhandling,
-                                               ch | SETXID_BITMASK, ch));
 }
 
 
 static void
 setxid_unmark_thread (struct xid_command *cmdp, struct pthread *t)
 {
-  int ch;
-
-  do
-    {
-      ch = t->cancelhandling;
-      if ((ch & SETXID_BITMASK) == 0)
-        return;
-    }
-  while (atomic_compare_and_exchange_bool_acq (&t->cancelhandling,
-                                               ch & ~SETXID_BITMASK, ch));
+  atomic_exchange_release (&t->setxid_flag, 0);
 
   /* Release the futex just in case.  */
   t->setxid_futex = 1;
@@ -154,7 +127,7 @@ setxid_unmark_thread (struct xid_command *cmdp, struct pthread *t)
 static int
 setxid_signal_thread (struct xid_command *cmdp, struct pthread *t)
 {
-  if ((t->cancelhandling & SETXID_BITMASK) == 0)
+  if (atomic_load_relaxed (&t->setxid_flag) == 0)
     return 0;
 
   int val;
diff --git a/nptl/pthread_create.c b/nptl/pthread_create.c
index 763e32bc3e..c00d6ae00c 100644
--- a/nptl/pthread_create.c
+++ b/nptl/pthread_create.c
@@ -541,7 +541,7 @@ start_thread (void *arg)
     advise_stack_range (pd->stackblock, pd->stackblock_size, (uintptr_t) pd,
 			pd->guardsize);
 
-  if (__glibc_unlikely (pd->cancelhandling & SETXID_BITMASK))
+  if (__glibc_unlikely (atomic_load_relaxed (&pd->setxid_flag) == 1))
     {
       /* Some other thread might call any of the setXid functions and expect
 	 us to reply.  In this case wait until we did that.  */
@@ -551,7 +551,7 @@ start_thread (void *arg)
 	   condition used in the surrounding loop (cancelhandling).  We need
 	   to check and document why this is correct.  */
 	futex_wait_simple (&pd->setxid_futex, 0, FUTEX_PRIVATE);
-      while (pd->cancelhandling & SETXID_BITMASK);
+      while (atomic_load_relaxed (&pd->setxid_flag) == 1);
 
       /* Reset the value so that the stack can be reused.  */
       pd->setxid_futex = 0;
-- 
2.30.2