[nginx] Core: free shared memory zones only after reconfiguration.

[Maxim Dounin]

details:   http://hg.nginx.org/nginx/rev/9ef704d8563a
branches:  
changeset: 7151:9ef704d8563a
user:      Maxim Dounin <mdounin at mdounin.ru>
date:      Tue Oct 17 19:52:16 2017 +0300
description:
Core: free shared memory zones only after reconfiguration.

This is what usually happens for zones no longer used in the new
configuration, but zones where size or tag were changed were freed
when creating new memory zones.  If reconfiguration failed (for
example, due to a conflicting listening socket), this resulted in a
segmentation fault in the master process.

Reported by Zhihua Cao,
http://mailman.nginx.org/pipermail/nginx-devel/2017-October/010536.html.

diffstat:

 src/core/ngx_cycle.c |  24 +++++++++++++++++-------
 1 files changed, 17 insertions(+), 7 deletions(-)

diffs (44 lines):

diff --git a/src/core/ngx_cycle.c b/src/core/ngx_cycle.c
--- a/src/core/ngx_cycle.c
+++ b/src/core/ngx_cycle.c
@@ -470,8 +470,6 @@ ngx_init_cycle(ngx_cycle_t *old_cycle)
                 goto shm_zone_found;
             }
 
-            ngx_shm_free(&oshm_zone[n].shm);
-
             break;
         }
 
@@ -662,14 +660,26 @@ ngx_init_cycle(ngx_cycle_t *old_cycle)
                 n = 0;
             }
 
-            if (oshm_zone[i].shm.name.len == shm_zone[n].shm.name.len
-                && ngx_strncmp(oshm_zone[i].shm.name.data,
-                               shm_zone[n].shm.name.data,
-                               oshm_zone[i].shm.name.len)
-                == 0)
+            if (oshm_zone[i].shm.name.len != shm_zone[n].shm.name.len) {
+                continue;
+            }
+
+            if (ngx_strncmp(oshm_zone[i].shm.name.data,
+                            shm_zone[n].shm.name.data,
+                            oshm_zone[i].shm.name.len)
+                != 0)
+            {
+                continue;
+            }
+
+            if (oshm_zone[i].tag == shm_zone[n].tag
+                && oshm_zone[i].shm.size == shm_zone[n].shm.size
+                && !oshm_zone[i].noreuse)
             {
                 goto live_shm_zone;
             }
+
+            break;
         }
 
         ngx_shm_free(&oshm_zone[i].shm);