Fix a race condition that can lead to deadlock in the memdb VFS if one

thread is trying to open an existing database at the same moment that
another thread that is the only prior user of that database is trying to
close it.

FossilOrigin-Name: b635375dbe22bd31c437ca574eb0c014c0b045de6cc0816c32d2ceceff9191fb

diff --git a/manifest b/manifest
index 6aa2c423a5b343c92d4fdcd247fa5fc10b2a7def..b9bb6e6b1bcd696405ff5e52a41b27e5e3ea2e17 100644 (file)
--- a/manifest
+++ b/manifest
@@ -1,5 +1,5 @@
-C Add\sthe\snew\sthreadtest5\stest\sprogram\sfor\sstressing\smultiple\sdatabase\nconnections\sin\sthe\ssame\sprocess\shammering\son\sa\ssingle\sdatabase.\nPrimarily\sdesigned\sto\stest\smemdb,\sbut\sworks\son\sany\sdatabase.
-D 2021-05-12T14:17:20.226
+C Fix\sa\srace\scondition\sthat\scan\slead\sto\sdeadlock\sin\sthe\smemdb\sVFS\sif\sone\nthread\sis\strying\sto\sopen\san\sexisting\sdatabase\sat\sthe\ssame\smoment\sthat\nanother\sthread\sthat\sis\sthe\sonly\sprior\suser\sof\sthat\sdatabase\sis\strying\sto\nclose\sit.
+D 2021-05-12T15:39:02.959
 F .fossil-settings/empty-dirs dbb81e8fc0401ac46a1491ab34a7f2c7c0452f2f06b54ebb845d024ca8283ef1
 F .fossil-settings/ignore-glob 35175cdfcf539b2318cb04a9901442804be81cd677d8b889fcc9149c21f239ea
 F LICENSE.md df5091916dbb40e6e9686186587125e1b2ff51f022cc334e886c19a0e9982724
@@ -514,7 +514,7 @@ F src/mem1.c c12a42539b1ba105e3707d0e628ad70e611040d8f5e38cf942cee30c867083de
 F src/mem2.c b93b8762ab999a29ae7751532dadf0a1ac78040308a5fb1d17fcc365171d67eb
 F src/mem3.c 30301196cace2a085cbedee1326a49f4b26deff0af68774ca82c1f7c06fda4f6
 F src/mem5.c 9bf955937b07f8c32541c8a9991f33ce3173d944
-F src/memdb.c 0c95e0299cc81e19d8695d2e7b81c338a5e77d083aa7849643eafcc2a3b1115a
+F src/memdb.c 41acf2b1a80a20b38a05f03711564b51c67e6dc376cc3f6b829ae644be25ad93
 F src/memjournal.c 431c70a111223a8a6e2e7e9f014afc6c88d818d357d866afc563195f2277d50e
 F src/msvc.h 3a15918220367a8876be3fa4f2abe423a861491e84b864fb2b7426bf022a28f8
 F src/mutex.c 5e3409715552348732e97b9194abe92fdfcd934cfb681df4ba0ab87ac6c18d25
@@ -1463,7 +1463,7 @@ F test/threadtest1.c 6029d9c5567db28e6dc908a0c63099c3ba6c383b
 F test/threadtest2.c a70a8e94bef23339d34226eb9521015ef99f4df8
 F test/threadtest3.c e63013af10cf236c7610eb06d33bde08c861806dc64be811940ff4d9ddd34a4f
 F test/threadtest4.c c1e67136ceb6c7ec8184e56ac61db28f96bd2925
-F test/threadtest5.c 9b4d782c58d8915d7e955ff8051f3d03628bda0d33b82971ea8c0f2f2808c421 w test/memdb-threads-1.c
+F test/threadtest5.c 9b4d782c58d8915d7e955ff8051f3d03628bda0d33b82971ea8c0f2f2808c421
 F test/time-wordcount.sh 8e0b0f8109367827ad5d58f5cc849705731e4b90
 F test/tkt-02a8e81d44.test 6c80d9c7514e2a42d4918bf87bf6bc54f379110c
 F test/tkt-18458b1a.test 6a62cb1ee50fa3c620da59e3a6f531eb38fceaf7e2166203816b724524e6f1d6
@@ -1913,7 +1913,7 @@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a91a7acc6293828957a386a8a93
 F vsixtest/vsixtest.vcxproj.data 2ed517e100c66dc455b492e1a33350c1b20fbcdc
 F vsixtest/vsixtest.vcxproj.filters 37e51ffedcdb064aad6ff33b6148725226cd608e
 F vsixtest/vsixtest_TemporaryKey.pfx e5b1b036facdb453873e7084e1cae9102ccc67a0
-P 533fffc4a39b01c3aba75bd3271fd6ccd9516d9681ed04adbe19bd7de03f4c16
-R 4fefc92ffd76e6c05a1532a9460cad0d
+P 8db1c06958b8e1691440d4fd392648b74a1940b721852dabd315005efad520fc
+R 1abbc8f5df29e63c759567b710531636
 U drh
-Z d3fbbeb2377b80ce42b7a7b26e8ca8a8
+Z 05516c08485b60e7b77e8989ba53becd

diff --git a/manifest.uuid b/manifest.uuid
index 9f7f95d086a456d584fcd28b1c547414f05db099..0057fec2eec8777bd644af36e5f184a5f343fdfa 100644 (file)
--- a/manifest.uuid
+++ b/manifest.uuid
@@ -1 +1 @@
-8db1c06958b8e1691440d4fd392648b74a1940b721852dabd315005efad520fc
\ No newline at end of file
+b635375dbe22bd31c437ca574eb0c014c0b045de6cc0816c32d2ceceff9191fb
\ No newline at end of file

diff --git a/src/memdb.c b/src/memdb.c
index d2509a7e3283b174658eef34e09c9ae691cbdb9d..b20d83bf030b6d2844ae71d2030d1c4b0dfa82c6 100644 (file)
--- a/src/memdb.c
+++ b/src/memdb.c
@@ -196,29 +196,33 @@ static void memdbLeave(MemStore *p){
 */
 static int memdbClose(sqlite3_file *pFile){
   MemStore *p = ((MemFile*)pFile)->pStore;
-  memdbEnter(p);
-  p->nRef--;
-  if( p->nRef<=0 ){
-    if( p->mFlags & SQLITE_DESERIALIZE_FREEONCLOSE ){
-      sqlite3_free(p->aData);
-    }
-    if( p->zFName ){
-      int i;
+  if( p->zFName ){
+    int i;
 #ifndef SQLITE_MUTEX_OMIT
-      sqlite3_mutex *pVfsMutex = sqlite3MutexAlloc(SQLITE_MUTEX_STATIC_VFS1);
+    sqlite3_mutex *pVfsMutex = sqlite3MutexAlloc(SQLITE_MUTEX_STATIC_VFS1);
 #endif
-      sqlite3_mutex_enter(pVfsMutex);
-      for(i=0; ALWAYS(i<memdb_g.nMemStore); i++){
-        if( memdb_g.apMemStore[i]==p ){
+    sqlite3_mutex_enter(pVfsMutex);
+    for(i=0; ALWAYS(i<memdb_g.nMemStore); i++){
+      if( memdb_g.apMemStore[i]==p ){
+        memdbEnter(p);
+        if( p->nRef==1 ){
           memdb_g.apMemStore[i] = memdb_g.apMemStore[--memdb_g.nMemStore];
           if( memdb_g.nMemStore==0 ){
             sqlite3_free(memdb_g.apMemStore);
             memdb_g.apMemStore = 0;
           }
-          break;
         }
+        break;
       }
-      sqlite3_mutex_leave(pVfsMutex);
+    }
+    sqlite3_mutex_leave(pVfsMutex);
+  }else{
+    memdbEnter(p);
+  }
+  p->nRef--;
+  if( p->nRef<=0 ){
+    if( p->mFlags & SQLITE_DESERIALIZE_FREEONCLOSE ){
+      sqlite3_free(p->aData);
     }
     memdbLeave(p);
     sqlite3_mutex_free(p->pMutex);