mdbx-posix: checking for file removal during LCK-seizing.

Change-Id: I7626ceda62fc4dac86323bec4194ae46bc19d9d3

src/elements/lck-posix.c

@@ -220,6 +220,65 @@ MDBX_INTERNAL_FUNC int mdbx_ipclock_destroy(mdbx_ipclock_t *ipc) {
 }
 #endif /* MDBX_LOCKING > MDBX_LOCKING_SYSV */
 
+static int check_fstat(MDBX_env *env) {
+  struct stat st;
+
+  int rc = MDBX_SUCCESS;
+  if (fstat(env->me_lazy_fd, &st)) {
+    rc = errno;
+    mdbx_error("fstat(%s), err %d", "DXB", rc);
+    return rc;
+  }
+
+  if (!S_ISREG(st.st_mode) || st.st_nlink < 1) {
+#ifdef EBADFD
+    rc = EBADFD;
+#else
+    rc = EPERM;
+#endif
+    mdbx_error("%s %s, err %d", "DXB",
+               (st.st_nlink < 1) ? "file was removed" : "not a regular file",
+               rc);
+    return rc;
+  }
+
+  if (st.st_size < (off_t)(MDBX_MIN_PAGESIZE * NUM_METAS)) {
+    mdbx_verbose("dxb-file is too short (%u), exclusive-lock needed",
+                 (unsigned)st.st_size);
+    rc = MDBX_RESULT_TRUE;
+  }
+
+  //----------------------------------------------------------------------------
+
+  if (fstat(env->me_lfd, &st)) {
+    rc = errno;
+    mdbx_error("fstat(%s), err %d", "LCK", rc);
+    return rc;
+  }
+
+  if (!S_ISREG(st.st_mode) || st.st_nlink < 1) {
+#ifdef EBADFD
+    rc = EBADFD;
+#else
+    rc = EPERM;
+#endif
+    mdbx_error("%s %s, err %d", "LCK",
+               (st.st_nlink < 1) ? "file was removed" : "not a regular file",
+               rc);
+    return rc;
+  }
+
+  /* Checking file size for detect the situation when we got the shared lock
+   * immediately after mdbx_lck_destroy(). */
+  if (st.st_size < (off_t)(sizeof(MDBX_lockinfo) + sizeof(MDBX_reader))) {
+    mdbx_verbose("lck-file is too short (%u), exclusive-lock needed",
+                 (unsigned)st.st_size);
+    rc = MDBX_RESULT_TRUE;
+  }
+
+  return rc;
+}
+
 MDBX_INTERNAL_FUNC int __cold mdbx_lck_seize(MDBX_env *env) {
   assert(env->me_lazy_fd != INVALID_HANDLE_VALUE);
   if (unlikely(mdbx_getpid() != env->me_pid))
@@ -229,7 +288,7 @@ MDBX_INTERNAL_FUNC int __cold mdbx_lck_seize(MDBX_env *env) {
     choice_fcntl();
 #endif /* MDBX_USE_OFDLOCKS */
 
-  int rc;
+  int rc = MDBX_SUCCESS;
   if (env->me_lfd == INVALID_HANDLE_VALUE) {
     /* LY: without-lck mode (e.g. exclusive or on read-only filesystem) */
     rc =
@@ -242,11 +301,27 @@ MDBX_INTERNAL_FUNC int __cold mdbx_lck_seize(MDBX_env *env) {
     }
     return MDBX_RESULT_TRUE /* Done: return with exclusive locking. */;
   }
+#if defined(_POSIX_PRIORITY_SCHEDULING) && _POSIX_PRIORITY_SCHEDULING > 0
+  sched_yield();
+#endif
+
+retry:
+  if (rc == MDBX_RESULT_TRUE) {
+    rc = lck_op(env->me_lfd, op_setlk, F_UNLCK, 0, 1);
+    if (rc != MDBX_SUCCESS) {
+      mdbx_error("%s, err %u", "unlock-before-retry", rc);
+      mdbx_assert(env, MDBX_IS_ERROR(rc));
+      return rc;
+    }
+  }
 
-retry_exclusive:
   /* Firstly try to get exclusive locking.  */
   rc = lck_op(env->me_lfd, op_setlk, F_WRLCK, 0, 1);
   if (rc == MDBX_SUCCESS) {
+    rc = check_fstat(env);
+    if (MDBX_IS_ERROR(rc))
+      return rc;
+
   continue_dxb_exclusive:
     rc =
         lck_op(env->me_lazy_fd, op_setlk,
@@ -254,6 +329,10 @@ retry_exclusive:
     if (rc == MDBX_SUCCESS)
       return MDBX_RESULT_TRUE /* Done: return with exclusive locking. */;
 
+    int err = check_fstat(env);
+    if (MDBX_IS_ERROR(err))
+      return err;
+
     /* the cause may be a collision with POSIX's file-lock recovery. */
     if (!(rc == EAGAIN || rc == EACCES || rc == EBUSY || rc == EWOULDBLOCK ||
           rc == EDEADLK)) {
@@ -263,6 +342,11 @@ retry_exclusive:
     }
 
     /* Fallback to lck-shared */
+  } else if (!(rc == EAGAIN || rc == EACCES || rc == EBUSY ||
+               rc == EWOULDBLOCK || rc == EDEADLK)) {
+    mdbx_error("%s, err %u", "try-exclusive", rc);
+    mdbx_assert(env, MDBX_IS_ERROR(rc));
+    return rc;
   }
 
   /* Here could be one of two:
@@ -282,6 +366,14 @@ retry_exclusive:
     return rc;
   }
 
+  rc = check_fstat(env);
+  if (rc == MDBX_RESULT_TRUE)
+    goto retry;
+  if (rc != MDBX_SUCCESS) {
+    mdbx_error("%s, err %u", "lck_fstat", rc);
+    return rc;
+  }
+
   /* got shared, retry exclusive */
   rc = lck_op(env->me_lfd, op_setlk, F_WRLCK, 0, 1);
   if (rc == MDBX_SUCCESS)
@@ -294,27 +386,6 @@ retry_exclusive:
     return rc;
   }
 
-  /* Checking file size for detect the situation when we got the shared lock
-   * immediately after mdbx_lck_destroy(). */
-  struct stat st;
-  if (fstat(env->me_lfd, &st)) {
-    rc = errno;
-    mdbx_error("%s(%s) failed: errcode %u", __func__, "check-filesize", rc);
-    mdbx_assert(env, MDBX_IS_ERROR(rc));
-    return rc;
-  }
-  if (st.st_size < (unsigned)(sizeof(MDBX_lockinfo) + sizeof(MDBX_reader))) {
-    mdbx_verbose("lck-file is too short (%u), retry exclusive-lock",
-                 (unsigned)st.st_size);
-    rc = lck_op(env->me_lfd, op_setlk, F_UNLCK, 0, 1);
-    if (rc != MDBX_SUCCESS) {
-      mdbx_error("%s(%s) failed: errcode %u", __func__, "retry-exclusive", rc);
-      mdbx_assert(env, MDBX_IS_ERROR(rc));
-      return rc;
-    }
-    goto retry_exclusive;
-  }
-
   /* Lock against another process operating in without-lck or exclusive mode. */
   rc =
       lck_op(env->me_lazy_fd, op_setlk,
@@ -357,10 +428,13 @@ MDBX_INTERNAL_FUNC int __cold mdbx_lck_destroy(MDBX_env *env,
     return MDBX_PANIC;
 
   int rc = MDBX_SUCCESS;
+  struct stat lck_info;
   if (env->me_lfd != INVALID_HANDLE_VALUE && !inprocess_neighbor &&
       env->me_lck &&
       /* try get exclusive access */
       lck_op(env->me_lfd, op_setlk, F_WRLCK, 0, OFF_T_MAX) == 0 &&
+      /* if LCK was not removed */
+      fstat(env->me_lfd, &lck_info) == 0 && lck_info.st_nlink > 0 &&
       lck_op(env->me_lazy_fd, op_setlk,
              (env->me_flags & MDBX_RDONLY) ? F_RDLCK : F_WRLCK, 0,
              OFF_T_MAX) == 0) {