From 6be12065deac51dabac8f38928139e207d98791a Mon Sep 17 00:00:00 2001
From: Yanfeng Liu <yfliu2008@qq.com>
Date: Mon, 27 May 2024 12:06:47 +0800
Subject: [PATCH] sched/signal: reclaim sigaction block after use

This adds logic to reclaim sigaction blocks to reduce memory footprint.

Signed-off-by: Yanfeng Liu <yfliu2008@qq.com>
---
 sched/signal/sig_action.c | 112 +++++++++++++++++++++++++++++++++++---
 sched/signal/signal.h     |   3 +-
 2 files changed, 106 insertions(+), 9 deletions(-)

diff --git a/sched/signal/sig_action.c b/sched/signal/sig_action.c
index 934a668224527..c0add08c99f21 100644
--- a/sched/signal/sig_action.c
+++ b/sched/signal/sig_action.c
@@ -50,12 +50,52 @@ static spinlock_t g_sigaction_spin;
  * Private Functions
  ****************************************************************************/
 
+/****************************************************************************
+ * Name: nxsig_add_freeaction
+ *
+ * Description:
+ *   Insert a signal action entry to the address-sorted free list
+ *
+ ****************************************************************************/
+
+static void nxsig_add_free(FAR sigactq_t *sigact)
+{
+  FAR sq_queue_t * const list = &g_sigfreeaction;
+  FAR sigactq_t *prev;
+  FAR sigactq_t *next;
+  irqstate_t flags;
+
+  flags = spin_lock_irqsave(&g_sigaction_spin);
+
+  if (list->head == NULL || (uintptr_t)sigact > (uintptr_t)list->tail)
+    {
+      sq_addlast((FAR sq_entry_t *)sigact, list);
+    }
+  else if ((uintptr_t)sigact < (uintptr_t)list->head)
+    {
+      sq_addfirst((FAR sq_entry_t *)sigact, list);
+    }
+  else
+    {
+      prev = (FAR sigactq_t *)list->head;
+      next = prev->flink;
+      while ((uintptr_t)next < (uintptr_t)sigact)
+        {
+          prev = next;
+          next = prev->flink;
+        }
+
+      sq_addafter((FAR sq_entry_t *)prev, (FAR sq_entry_t *)sigact, list);
+    }
+
+  spin_unlock_irqrestore(&g_sigaction_spin, flags);
+}
+
 /****************************************************************************
  * Name: nxsig_alloc_actionblock
  *
  * Description:
- *   Allocate a block of signal actions and place them
- *   on the free list.
+ *   Allocate a block of signal actions and place them in the free list.
  *
  ****************************************************************************/
 
@@ -67,14 +107,16 @@ static void nxsig_alloc_actionblock(void)
 
   /* Allocate a block of signal actions */
 
-  sigact = kmm_malloc((sizeof(sigactq_t)) * NUM_SIGNAL_ACTIONS);
+  sigact = kmm_zalloc((sizeof(sigactq_t)) * NUM_SIGNAL_ACTIONS);
   if (sigact != NULL)
     {
+      sigact->sob = 1;        /* mark the first entry only */
+      nxsig_add_free(sigact);
       flags = spin_lock_irqsave(&g_sigaction_spin);
-
-      for (i = 0; i < NUM_SIGNAL_ACTIONS; i++)
+      for (i = 1; i < NUM_SIGNAL_ACTIONS; i++)
         {
-          sq_addlast((FAR sq_entry_t *)sigact++, &g_sigfreeaction);
+          sq_addafter((FAR sq_entry_t *)(sigact + i - 1),
+                      (FAR sq_entry_t *)(sigact + i), &g_sigfreeaction);
         }
 
       spin_unlock_irqrestore(&g_sigaction_spin, flags);
@@ -407,11 +449,65 @@ int sigaction(int signo, FAR const struct sigaction *act,
 
 void nxsig_release_action(FAR sigactq_t *sigact)
 {
+  FAR sq_queue_t * const list = &g_sigfreeaction;
+  FAR sigactq_t *prev;
+  FAR sigactq_t *next;
   irqstate_t flags;
+  int i;
+
+  /* Put back to the free list */
+
+  nxsig_add_free(sigact);
 
-  /* Just put it back on the free list */
+  /* Scan the list for complete blocks */
 
   flags = spin_lock_irqsave(&g_sigaction_spin);
-  sq_addlast((FAR sq_entry_t *)sigact, &g_sigfreeaction);
+
+  prev = NULL;
+  sigact = (FAR sigactq_t *)list->head;
+
+next_sob:
+
+  while (sigact && !sigact->sob)         /* Seek for SOB entry */
+    {
+      prev = sigact;
+      sigact = sigact->flink;
+    }
+
+  if (sigact && sigact->flink)
+    {
+      for (next = sigact->flink, i = 1;  /* Check following entries */
+           next == sigact + i && i < NUM_SIGNAL_ACTIONS;
+           next = next->flink, i++);
+
+      if (i == NUM_SIGNAL_ACTIONS)       /* Got complete block */
+        {
+          for (; i > 0; i--)             /* Detach entries from list */
+            {
+              if (!prev)
+                {
+                  sq_remfirst(list);
+                }
+              else
+                {
+                  sq_remafter((FAR sq_entry_t *)prev, list);
+                }
+            }
+
+          kmm_free(sigact);              /* Reclaim the block */
+
+          if (list->head && next)
+            {
+              sigact = next;
+            }
+        }
+      else                               /* Advance i entries */
+        {
+          for (; i > 0; i--, prev = sigact, sigact = sigact->flink);
+        }
+
+      goto next_sob;
+    }
+
   spin_unlock_irqrestore(&g_sigaction_spin, flags);
 }
diff --git a/sched/signal/signal.h b/sched/signal/signal.h
index 0553b8e3b0f5e..bf1535299a943 100644
--- a/sched/signal/signal.h
+++ b/sched/signal/signal.h
@@ -65,7 +65,8 @@ struct sigactq
 {
   FAR struct sigactq *flink;     /* Forward link */
   struct sigaction act;          /* Sigaction data */
-  uint8_t   signo;               /* Signal associated with action */
+  uint8_t   signo:7;             /* Signal associated with action */
+  uint8_t   sob:1;               /* Flag depicting start entry of a block */
 };
 typedef struct sigactq  sigactq_t;