Update TODO list regarding non-queuing of signal actions; Add comments in code at areas where the issue applies.

TODO

@@ -13,7 +13,7 @@ nuttx/:
   (5)  SMP
   (1)  Memory Management (mm/)
   (0)  Power Management (drivers/pm)
-  (3)  Signals (sched/signal, arch/)
+  (4)  Signals (sched/signal, arch/)
   (2)  pthreads (sched/pthread)
   (0)  Message Queues (sched/mqueue)
  (10)  Kernel/Protected Build
@@ -763,6 +763,22 @@ o Signals (sched/signal, arch/)
   Status:      Open
   Priority:    Low. Even if there are only 31 usable signals, that is still a lot.
 
+  Title:       NO QUEUING of SIGNAL ACTIONS
+  Description: In the architecture specific implemenation of struct xcptcontext,
+               there are fields used by signal handling logic to pass the state
+               information needed to dispatch signal actions to the appropriate
+               handler.
+
+               There is only one copy of this state information in the
+               implementations of struct xcptcontext and, as a consequence,
+               if there is a signal handler executing on a thread, then addition
+               signal actions will be lost until that signal handler completes
+               and releases those resources.
+  Status:      Open
+  Priority:    Low.  This design flaw has been around for ages and no one has yet
+               complained about it.  Apparently the visibility of the problem is
+               very low.
+
 o pthreads (sched/pthreads)
   ^^^^^^^^^^^^^^^^^^^^^^^^^
 

arch/arm/include/arm/irq.h

@@ -138,15 +138,20 @@
 #ifndef __ASSEMBLY__
 struct xcptcontext
 {
+#ifndef CONFIG_DISABLE_SIGNALS
   /* The following function pointer is non-zero if there
    * are pending signals to be processed.
    */
 
-#ifndef CONFIG_DISABLE_SIGNALS
   void *sigdeliver; /* Actual type is sig_deliver_t */
 
   /* These are saved copies of LR and CPSR used during
    * signal processing.
+   *
+   * REVISIT:  Because there is only one copy of these save areas,
+   * only a single signal handler can be active.  This precludes
+   * queuing of signal actions.  As a result, signals received while
+   * another signal handler is executing will be ignored!
    */
 
   uint32_t saved_pc;

arch/arm/include/armv6-m/irq.h

@@ -173,6 +173,11 @@ struct xcptcontext
 
   /* These are saved copies of LR, PRIMASK, and xPSR used during
    * signal processing.
+   *
+   * REVISIT:  Because there is only one copy of these save areas,
+   * only a single signal handler can be active.  This precludes
+   * queuing of signal actions.  As a result, signals received while
+   * another signal handler is executing will be ignored!
    */
 
   uint32_t saved_pc;

arch/arm/include/armv7-a/irq.h

@@ -229,14 +229,20 @@ struct xcpt_syscall_s
 #ifndef __ASSEMBLY__
 struct xcptcontext
 {
+#ifndef CONFIG_DISABLE_SIGNALS
   /* The following function pointer is non-zero if there are pending signals
    * to be processed.
    */
 
-#ifndef CONFIG_DISABLE_SIGNALS
   void *sigdeliver; /* Actual type is sig_deliver_t */
 
-  /* These are saved copies of LR and CPSR used during signal processing. */
+  /* These are saved copies of LR and CPSR used during signal processing.
+   *
+   * REVISIT:  Because there is only one copy of these save areas,
+   * only a single signal handler can be active.  This precludes
+   * queuing of signal actions.  As a result, signals received while
+   * another signal handler is executing will be ignored!
+   */
 
   uint32_t saved_pc;
   uint32_t saved_cpsr;

arch/arm/include/armv7-m/irq.h

@@ -128,6 +128,11 @@ struct xcptcontext
 
   /* These are saved copies of LR, PRIMASK, and xPSR used during
    * signal processing.
+   *
+   * REVISIT:  Because there is only one copy of these save areas,
+   * only a single signal handler can be active.  This precludes
+   * queuing of signal actions.  As a result, signals received while
+   * another signal handler is executing will be ignored!
    */
 
   uint32_t saved_pc;

arch/arm/include/armv7-r/irq.h

@@ -229,14 +229,20 @@ struct xcpt_syscall_s
 #ifndef __ASSEMBLY__
 struct xcptcontext
 {
+#ifndef CONFIG_DISABLE_SIGNALS
   /* The following function pointer is non-zero if there are pending signals
    * to be processed.
    */
 
-#ifndef CONFIG_DISABLE_SIGNALS
   void *sigdeliver; /* Actual type is sig_deliver_t */
 
-  /* These are saved copies of LR and CPSR used during signal processing. */
+  /* These are saved copies of LR and CPSR used during signal processing.
+   *
+   * REVISIT:  Because there is only one copy of these save areas,
+   * only a single signal handler can be active.  This precludes
+   * queuing of signal actions.  As a result, signals received while
+   * another signal handler is executing will be ignored!
+   */
 
   uint32_t saved_pc;
   uint32_t saved_cpsr;

arch/avr/include/avr/irq.h

@@ -106,14 +106,20 @@
 #ifndef __ASSEMBLY__
 struct xcptcontext
 {
+#ifndef CONFIG_DISABLE_SIGNALS
   /* The following function pointer is non-zero if there are pending signals
    * to be processed.
    */
 
-#ifndef CONFIG_DISABLE_SIGNALS
   void *sigdeliver; /* Actual type is sig_deliver_t */
 
-  /* These are saved copies of PC and SR used during signal processing.*/
+  /* These are saved copies of PC and SR used during signal processing.
+   *
+   * REVISIT:  Because there is only one copy of these save areas,
+   * only a single signal handler can be active.  This precludes
+   * queuing of signal actions.  As a result, signals received while
+   * another signal handler is executing will be ignored!
+   */
 
   uint8_t saved_pc1;
   uint8_t saved_pc0;

arch/avr/include/avr32/irq.h

@@ -107,14 +107,20 @@
 #ifndef __ASSEMBLY__
 struct xcptcontext
 {
+#ifndef CONFIG_DISABLE_SIGNALS
   /* The following function pointer is non-zero if there are pending signals
    * to be processed.
    */
 
-#ifndef CONFIG_DISABLE_SIGNALS
   void *sigdeliver; /* Actual type is sig_deliver_t */
 
-  /* These are saved copies of PC and SR used during signal processing.*/
+  /* These are saved copies of PC and SR used during signal processing.
+   *
+   * REVISIT:  Because there is only one copy of these save areas,
+   * only a single signal handler can be active.  This precludes
+   * queuing of signal actions.  As a result, signals received while
+   * another signal handler is executing will be ignored!
+   */
 
   uint32_t saved_pc;
   uint32_t saved_sr;

arch/mips/include/mips32/irq.h

@@ -338,6 +338,11 @@ struct xcptcontext
 
   /* These additional register save locations are used to implement the
    * signal delivery trampoline.
+   *
+   * REVISIT:  Because there is only one copy of these save areas,
+   * only a single signal handler can be active.  This precludes
+   * queuing of signal actions.  As a result, signals received while
+   * another signal handler is executing will be ignored!
    */
 
   uint32_t saved_epc;    /* Trampoline PC */

arch/misoc/include/lm32/irq.h

@@ -204,6 +204,11 @@ struct xcptcontext
 
   /* These additional register save locations are used to implement the
    * signal delivery trampoline.
+   *
+   * REVISIT:  Because there is only one copy of these save areas,
+   * only a single signal handler can be active.  This precludes
+   * queuing of signal actions.  As a result, signals received while
+   * another signal handler is executing will be ignored!
    */
 
   uint32_t saved_epc;     /* Trampoline PC */

arch/or1k/include/mor1kx/irq.h

@@ -171,15 +171,20 @@ struct xcptcontext
 
   uint32_t regs[XCPTCONTEXT_REGS];
 
+#ifndef CONFIG_DISABLE_SIGNALS
   /* The following function pointer is non-zero if there
    * are pending signals to be processed.
    */
 
-#ifndef CONFIG_DISABLE_SIGNALS
   void *sigdeliver; /* Actual type is sig_deliver_t */
 
   /* These are saved copies of LR and CPSR used during
    * signal processing.
+   *
+   * REVISIT:  Because there is only one copy of these save areas,
+   * only a single signal handler can be active.  This precludes
+   * queuing of signal actions.  As a result, signals received while
+   * another signal handler is executing will be ignored!
    */
 
   uint32_t saved_pc;

arch/renesas/include/m16c/irq.h

@@ -242,14 +242,20 @@
 #ifndef __ASSEMBLY__
 struct xcptcontext
 {
+#ifndef CONFIG_DISABLE_SIGNALS
   /* The following function pointer is non-zero if there are pending signals
    * to be processed.
    */
 
-#ifndef CONFIG_DISABLE_SIGNALS
   void *sigdeliver; /* Actual type is sig_deliver_t */
 
-  /* These are saved copies of LR and SR used during signal processing. */
+  /* These are saved copies of LR and SR used during signal processing.
+   *
+   * REVISIT:  Because there is only one copy of these save areas,
+   * only a single signal handler can be active.  This precludes
+   * queuing of signal actions.  As a result, signals received while
+   * another signal handler is executing will be ignored!
+   */
 
   uint8_t saved_pc[2];
   uint8_t saved_flg;

arch/renesas/include/sh1/irq.h

@@ -459,14 +459,20 @@
 #ifndef __ASSEMBLY__
 struct xcptcontext
 {
+#ifndef CONFIG_DISABLE_SIGNALS
   /* The following function pointer is non-zero if there are pending signals
    * to be processed.
    */
 
-#ifndef CONFIG_DISABLE_SIGNALS
   void *sigdeliver; /* Actual type is sig_deliver_t */
 
-  /* These are saved copies of LR and SR used during signal processing. */
+  /* These are saved copies of LR and SR used during signal processing.
+   *
+   * REVISIT:  Because there is only one copy of these save areas,
+   * only a single signal handler can be active.  This precludes
+   * queuing of signal actions.  As a result, signals received while
+   * another signal handler is executing will be ignored!
+   */
 
   uint32_t saved_pc;
   uint32_t saved_sr;

arch/risc-v/include/rv32im/irq.h

@@ -312,6 +312,11 @@ struct xcptcontext
 
   /* These additional register save locations are used to implement the
    * signal delivery trampoline.
+   *
+   * REVISIT:  Because there is only one copy of these save areas,
+   * only a single signal handler can be active.  This precludes
+   * queuing of signal actions.  As a result, signals received while
+   * another signal handler is executing will be ignored!
    */
 
   uint32_t saved_epc;     /* Trampoline PC */

arch/x86/include/i486/irq.h

@@ -166,15 +166,20 @@
 #ifndef __ASSEMBLY__
 struct xcptcontext
 {
+#ifndef CONFIG_DISABLE_SIGNALS
   /* The following function pointer is non-zero if there are pending signals
    * to be processed.
    */
 
-#ifndef CONFIG_DISABLE_SIGNALS
   void *sigdeliver; /* Actual type is sig_deliver_t */
 
   /* These are saved copies of instruction pointer and EFLAGS used during
    * signal processing.
+   *
+   * REVISIT:  Because there is only one copy of these save areas,
+   * only a single signal handler can be active.  This precludes
+   * queuing of signal actions.  As a result, signals received while
+   * another signal handler is executing will be ignored!
    */
 
   uint32_t saved_eip;

arch/xtensa/include/irq.h

@@ -146,14 +146,20 @@
 
 struct xcptcontext
 {
+#ifndef CONFIG_DISABLE_SIGNALS
   /* The following function pointer is non-zero if there are pending signals
    * to be processed.
    */
 
-#ifndef CONFIG_DISABLE_SIGNALS
   void *sigdeliver; /* Actual type is sig_deliver_t */
 
-  /* These are saved copies of registers used during signal processing. */
+  /* These are saved copies of registers used during signal processing.
+   *
+   * REVISIT:  Because there is only one copy of these save areas,
+   * only a single signal handler can be active.  This precludes
+   * queuing of signal actions.  As a result, signals received while
+   * another signal handler is executing will be ignored!
+   */
 
   uint32_t saved_pc;
   uint32_t saved_ps;

arch/z16/include/z16f/irq.h

@@ -178,14 +178,20 @@ struct xcptcontext
 
   uint16_t regs[XCPTCONTEXT_REGS];
 
+#ifndef CONFIG_DISABLE_SIGNALS
   /* The following function pointer is non-zero if there
    * are pending signals to be processed.
    */
 
-#ifndef CONFIG_DISABLE_SIGNALS
   CODE void *sigdeliver; /* Actual type is sig_deliver_t */
 
-  /* The following retains that state during signal execution */
+  /* The following retains that state during signal execution.
+   *
+   * REVISIT:  Because there is only one copy of these save areas,
+   * only a single signal handler can be active.  This precludes
+   * queuing of signal actions.  As a result, signals received while
+   * another signal handler is executing will be ignored!
+   */
 
   uint32_t saved_pc;  /* Saved return address */
   uint16_t saved_i;   /* Saved interrupt state */

arch/z80/include/ez80/irq.h

@@ -213,14 +213,20 @@ struct xcptcontext
 
   chipreg_t regs[XCPTCONTEXT_REGS];
 
+#ifndef CONFIG_DISABLE_SIGNALS
   /* The following function pointer is non-zero if there
    * are pending signals to be processed.
    */
 
-#ifndef CONFIG_DISABLE_SIGNALS
   CODE void *sigdeliver; /* Actual type is sig_deliver_t */
 
-  /* The following retains that state during signal execution */
+  /* The following retains that state during signal execution
+   *
+   * REVISIT:  Because there is only one copy of these save areas,
+   * only a single signal handler can be active.  This precludes
+   * queuing of signal actions.  As a result, signals received while
+   * another signal handler is executing will be ignored!
+   */
 
   chipreg_t saved_pc;    /* Saved return address */
   chipreg_t saved_i;     /* Saved interrupt state */

arch/z80/include/z180/irq.h

@@ -186,14 +186,20 @@ struct xcptcontext
 
   chipreg_t regs[XCPTCONTEXT_REGS];
 
+#ifndef CONFIG_DISABLE_SIGNALS
   /* The following function pointer is non-zero if there
    * are pending signals to be processed.
    */
 
-#ifndef CONFIG_DISABLE_SIGNALS
   CODE void *sigdeliver; /* Actual type is sig_deliver_t */
 
-  /* The following retains that state during signal execution */
+  /* The following retains that state during signal execution
+   *
+   * REVISIT:  Because there is only one copy of these save areas,
+   * only a single signal handler can be active.  This precludes
+   * queuing of signal actions.  As a result, signals received while
+   * another signal handler is executing will be ignored!
+   */
 
   uint16_t saved_pc;    /* Saved return address */
   uint16_t saved_i;     /* Saved interrupt state */

arch/z80/include/z8/irq.h

@@ -319,17 +319,23 @@ struct xcptcontext
 
   chipreg_t regs[XCPTCONTEXT_REGS];
 
+#ifndef CONFIG_DISABLE_SIGNALS
   /* The following function pointer is non-zero if there
    * are pending signals to be processed.
    */
 
-#ifndef CONFIG_DISABLE_SIGNALS
-  CODE void *sigdeliver; 	/* Actual type is sig_deliver_t */
+  CODE void *sigdeliver;    /* Actual type is sig_deliver_t */
 
-  /* The following retains that state during signal execution */
+  /* The following retains that state during signal execution
+   *
+   * REVISIT:  Because there is only one copy of these save areas,
+   * only a single signal handler can be active.  This precludes
+   * queuing of signal actions.  As a result, signals received while
+   * another signal handler is executing will be ignored!
+   */
 
-  uint16_t saved_pc;		/* Saved return address */
-  uint16_t saved_irqctl;	/* Saved interrupt state */
+  uint16_t saved_pc;        /* Saved return address */
+  uint16_t saved_irqctl;    /* Saved interrupt state */
 #endif
 };
 #endif

arch/z80/include/z80/irq.h

@@ -103,14 +103,20 @@ struct xcptcontext
 
   chipreg_t regs[XCPTCONTEXT_REGS];
 
+#ifndef CONFIG_DISABLE_SIGNALS
   /* The following function pointer is non-zero if there
    * are pending signals to be processed.
    */
 
-#ifndef CONFIG_DISABLE_SIGNALS
   CODE void *sigdeliver; /* Actual type is sig_deliver_t */
 
-  /* The following retains that state during signal execution */
+  /* The following retains that state during signal execution.
+   *
+   * REVISIT:  Because there is only one copy of these save areas,
+   * only a single signal handler can be active.  This precludes
+   * queuing of signal actions.  As a result, signals received while
+   * another signal handler is executing will be ignored!
+   */
 
   uint16_t saved_pc;    /* Saved return address */
   uint16_t saved_i;     /* Saved interrupt state */