[04/15] nptl: Move setxid flag out of cancelhandling

Message ID 20210930200051.1017457-5-adhemerval.zanella@linaro.org
State New
Headers show
Series
  • Fix various NPTL synchronization issues
Related show

Commit Message

Carlos O'Donell via Libc-alpha Sept. 30, 2021, 8 p.m.
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          |  6 ++---
 nptl/nptl_setxid.c    | 55 ++++++++++++++-----------------------------
 nptl/pthread_create.c |  4 ++--
 4 files changed, 26 insertions(+), 42 deletions(-)

-- 
2.30.2

Patch

diff --git a/nptl/allocatestack.c b/nptl/allocatestack.c
index fa8100719f..74a8bbc19c 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.  */
@@ -303,6 +304,7 @@  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.  */
@@ -424,6 +426,7 @@  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 76522b85b3..db011af500 100644
--- a/nptl/descr.h
+++ b/nptl/descr.h
@@ -296,9 +296,6 @@  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;
@@ -338,6 +335,9 @@  struct pthread
   /* Lock to synchronize access to the descriptor.  */
   int lock;
 
+  /* Indicate whether thread is supposed to change XID, it acts a boolean
+     variable (0 means no operation pending).  */
+  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 1bd7b5f803..244536260d 100644
--- a/nptl/nptl_setxid.c
+++ b/nptl/nptl_setxid.c
@@ -75,14 +75,7 @@  __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;
@@ -96,8 +89,6 @@  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))
@@ -108,41 +99,31 @@  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
+  /* If thread is exiting right now, ignore it.  */
+  if (atomic_load_acquire (&t->joinstate) == THREAD_STATE_EXITING)
     {
-      ch = t->cancelhandling;
-
-      /* 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_load_relaxed (&t->setxid_flag) == 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_store_release (&t->setxid_flag, 0);
 
   /* Release the futex just in case.  */
   t->setxid_futex = 1;
@@ -153,7 +134,7 @@  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 c7d53edbb8..3659f51c46 100644
--- a/nptl/pthread_create.c
+++ b/nptl/pthread_create.c
@@ -562,7 +562,7 @@  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.  */
@@ -572,7 +572,7 @@  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;