nptl: Handle spurious EINTR when thread cancellation is disabled (BZ#29029)

Some Linux interfaces never restart after being interrupted by a signal
handler, regardless of the use of SA_RESTART [1].  It means that for
pthread cancellation, if the target thread disables cancellation with
pthread_setcancelstate and calls such interfaces (like poll or select),
it should not see spurious EINTR failures due the internal SIGCANCEL.

However recent changes made pthread_cancel to always sent the internal
signal, regardless of the target thread cancellation status or type.
To fix it, the previous semantic is restored, where the cancel signal
is only sent if the target thread has cancelation enabled in
asynchronous mode.

The cancel state and cancel type is moved back to cancelhandling
and atomic operation are used to synchronize between threads.  The
patch essentially revert the following commits:

  8c1c0aae20 nptl: Move cancel type out of cancelhandling
  2b51742531 nptl: Move cancel state out of cancelhandling
  26cfbb7162 nptl: Remove CANCELING_BITMASK

However I changed the atomic operation to follow the internal C11
semantic and removed the MACRO usage, it simplifies a bit the
resulting code (and removes another usage of the old atomic macros).

Checked on x86_64-linux-gnu, i686-linux-gnu, aarch64-linux-gnu,
and powerpc64-linux-gnu.

[1] https://man7.org/linux/man-pages/man7/signal.7.html

Reviewed-by: Florian Weimer <fweimer@redhat.com>
Tested-by: Aurelien Jarno <aurelien@aurel32.net>

1 files changed, 29 insertions, 12 deletions

diff --git a/nptl/descr.h b/nptl/descr.h
index ea8aca08e6..bb46b5958e 100644
--- a/nptl/descr.h
+++ b/nptl/descr.h
@@ -279,18 +279,27 @@ struct pthread
 
   /* Flags determining processing of cancellation.  */
   int cancelhandling;
+  /* Bit set if cancellation is disabled.  */
+#define CANCELSTATE_BIT		0
+#define CANCELSTATE_BITMASK	(1 << CANCELSTATE_BIT)
+  /* Bit set if asynchronous cancellation mode is selected.  */
+#define CANCELTYPE_BIT		1
+#define CANCELTYPE_BITMASK	(1 << CANCELTYPE_BIT)
+  /* Bit set if canceling has been initiated.  */
+#define CANCELING_BIT		2
+#define CANCELING_BITMASK	(1 << CANCELING_BIT)
   /* Bit set if canceled.  */
 #define CANCELED_BIT		3
-#define CANCELED_BITMASK	(0x01 << CANCELED_BIT)
+#define CANCELED_BITMASK	(1 << CANCELED_BIT)
   /* Bit set if thread is exiting.  */
 #define EXITING_BIT		4
-#define EXITING_BITMASK		(0x01 << EXITING_BIT)
+#define EXITING_BITMASK		(1 << EXITING_BIT)
   /* Bit set if thread terminated and TCB is freed.  */
 #define TERMINATED_BIT		5
-#define TERMINATED_BITMASK	(0x01 << TERMINATED_BIT)
+#define TERMINATED_BITMASK	(1 << TERMINATED_BIT)
   /* Bit set if thread is supposed to change XID.  */
 #define SETXID_BIT		6
-#define SETXID_BITMASK		(0x01 << SETXID_BIT)
+#define SETXID_BITMASK		(1 << SETXID_BIT)
 
   /* Flags.  Including those copied from the thread attribute.  */
   int flags;
@@ -390,14 +399,6 @@ struct pthread
   /* Indicates whether is a C11 thread created by thrd_creat.  */
   bool c11;
 
-  /* Thread cancel state (PTHREAD_CANCEL_ENABLE or
-     PTHREAD_CANCEL_DISABLE).  */
-  unsigned char cancelstate;
-
-  /* Thread cancel type (PTHREAD_CANCEL_DEFERRED or
-     PTHREAD_CANCEL_ASYNCHRONOUS).  */
-  unsigned char canceltype;
-
   /* Used in __pthread_kill_internal to detected a thread that has
      exited or is about to exit.  exit_lock must only be acquired
      after blocking signals.  */
@@ -417,6 +418,22 @@ struct pthread
   (sizeof (struct pthread) - offsetof (struct pthread, end_padding))
 } __attribute ((aligned (TCB_ALIGNMENT)));
 
+static inline bool
+cancel_enabled_and_canceled (int value)
+{
+  return (value & (CANCELSTATE_BITMASK | CANCELED_BITMASK | EXITING_BITMASK
+		   | TERMINATED_BITMASK))
+    == CANCELED_BITMASK;
+}
+
+static inline bool
+cancel_enabled_and_canceled_and_async (int value)
+{
+  return ((value) & (CANCELSTATE_BITMASK | CANCELTYPE_BITMASK | CANCELED_BITMASK
+		     | EXITING_BITMASK | TERMINATED_BITMASK))
+    == (CANCELTYPE_BITMASK | CANCELED_BITMASK);
+}
+
 /* This yields the pointer that TLS support code calls the thread pointer.  */
 #if TLS_TCB_AT_TP
 # define TLS_TPADJ(pd) (pd)