Use extra locks to prevent a readonly_shm=1 process from connecting to a

WAL-mode database if there are no writers.

FossilOrigin-Name: 35d979082b4ab36d6a8975f8f15a50e69f46b72a173164d2b353377b9f758bd8

diff --git a/manifest b/manifest
index a593818258106c98e8f6545f7dfa684f71f35dad..bf7be72e5e472a1336bd989632c771a0ba929625 100644 (file)
--- a/manifest
+++ b/manifest
@@ -1,5 +1,5 @@
-C Fix\sthe\ssqlite3_dbpage\svirtual\stable\sso\sthat\sit\scan\sread\sand\swrite\sfrom\nany\sattached\sdatabase.
-D 2017-10-25T19:18:33.009
+C Use\sextra\slocks\sto\sprevent\sa\sreadonly_shm=1\sprocess\sfrom\sconnecting\sto\sa\nWAL-mode\sdatabase\sif\sthere\sare\sno\swriters.
+D 2017-10-25T23:28:13.771
 F Makefile.in e016061b23e60ac9ec27c65cb577292b6bde0307ca55abd874ab3487b3b1beb2
 F Makefile.linux-gcc 7bc79876b875010e8c8f9502eb935ca92aa3c434
 F Makefile.msc 37740aba9c4bb359c627eadccf1cfd7be4f5f847078723777ea7763969e533b1
@@ -447,7 +447,7 @@ F src/os.c 22d31db3ca5a96a408fbf1ceeaaebcaf64c87024d2ff9fe1cf2ddbec3e75c104
 F src/os.h 48388821692e87da174ea198bf96b1b2d9d83be5dfc908f673ee21fafbe0d432
 F src/os_common.h b2f4707a603e36811d9b1a13278bffd757857b85
 F src/os_setup.h 0dbaea40a7d36bf311613d31342e0b99e2536586
-F src/os_unix.c 7edc872747feaa3016bd04e5e4389743bacafc0fee3444b0ecdec5d8f45049df
+F src/os_unix.c bec568f6f89e57b987f5ca38ae90087687d8e18669cd37eceb48ca6b56a8fbfb
 F src/os_win.c 6892c3ff23b7886577e47f13d827ca220c0831bae3ce00eea8c258352692f8c6
 F src/os_win.h 7b073010f1451abe501be30d12f6bc599824944a
 F src/pager.c 07cf850241667874fcce9d7d924c814305e499b26c804322e2261247b5921903
@@ -465,7 +465,7 @@ F src/resolve.c 5a461643f294ec510ca615b67256fc3861e4c8eff5f29e5940491e70553b1955
 F src/rowset.c 7b7e7e479212e65b723bf40128c7b36dc5afdfac
 F src/select.c e6a068d9ea54417d625578086d3d482284af8d5a449bb3593d40c257080806a8
 F src/shell.c.in f13262c8778f0cd76bf8d9c01bbf5ef66842e6b14e1705cd60d86ab32a6ce69f
-F src/sqlite.h.in ab4f8a29d1580dfaeb6891fa1b83cff8229ba0daa56994707ceaca71495d9ab7
+F src/sqlite.h.in ba9029e71a605bc5f236cd693abeb7920285785f2e1a92313ecf8fb1c9f52a86
 F src/sqlite3.rc 5121c9e10c3964d5755191c80dd1180c122fc3a8
 F src/sqlite3ext.h c02d628cca67f3889c689d82d25c3eb45e2c155db08e4c6089b5840d64687d34
 F src/sqliteInt.h 6f93fd6fde862410ac26b930f70752c38ad99ea78c3fc28356bac78049c53bd9
@@ -1666,7 +1666,10 @@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a91a7acc6293828957a386a8a93
 F vsixtest/vsixtest.vcxproj.data 2ed517e100c66dc455b492e1a33350c1b20fbcdc
 F vsixtest/vsixtest.vcxproj.filters 37e51ffedcdb064aad6ff33b6148725226cd608e
 F vsixtest/vsixtest_TemporaryKey.pfx e5b1b036facdb453873e7084e1cae9102ccc67a0
-P d6130cd226c0ca95e02f0cbabfdc27071acdcf83e0d0cb0eaa47d992479ed9a1
-R de06ad2d264283eba96aba95f64ee6f5
+P d4f893e1ae53a0445939ea2920af87d21dd36270494381028b2eaebe5c188f18
+R 7c17d54c5cff309a6f13f49dd620b485
+T *branch * readonly-wal-recovery
+T *sym-readonly-wal-recovery *
+T -sym-trunk *
 U drh
-Z 3b4d77a61659a96790923a30bda00b59
+Z 26f9af4fe6668c97b92039b43092c035

diff --git a/manifest.uuid b/manifest.uuid
index ce16a7caf02bf690a9310dcda55c40f7ce80ed99..44570bf71c6acb1d0b51c2b07c53279b3d089e80 100644 (file)
--- a/manifest.uuid
+++ b/manifest.uuid
@@ -1 +1 @@
-d4f893e1ae53a0445939ea2920af87d21dd36270494381028b2eaebe5c188f18
\ No newline at end of file
+35d979082b4ab36d6a8975f8f15a50e69f46b72a173164d2b353377b9f758bd8
\ No newline at end of file

diff --git a/src/os_unix.c b/src/os_unix.c
index c33d21fd9bcf7cb8cdd15cacd512a7e9e2c1b136..dadfaf990800ae4b1d2d23e7eebe7c76342f526e 100644 (file)
--- a/src/os_unix.c
+++ b/src/os_unix.c
@@ -4145,6 +4145,7 @@ struct unixShm {
 */
 #define UNIX_SHM_BASE   ((22+SQLITE_SHM_NLOCK)*4)         /* first lock byte */
 #define UNIX_SHM_DMS    (UNIX_SHM_BASE+SQLITE_SHM_NLOCK)  /* deadman switch */
+#define UNIX_SHM_N_DMS  1000000000                        /* Size of the DMS */
 
 /*
 ** Apply posix advisory locks for all bytes from ofst through ofst+n-1.
@@ -4166,12 +4167,6 @@ static int unixShmSystemLock(
   pShmNode = pFile->pInode->pShmNode;
   assert( sqlite3_mutex_held(pShmNode->mutex) || pShmNode->nRef==0 );
 
-  /* Shared locks never span more than one byte */
-  assert( n==1 || lockType!=F_RDLCK );
-
-  /* Locks are within range */
-  assert( n>=1 && n<=SQLITE_SHM_NLOCK );
-
   if( pShmNode->h>=0 ){
     /* Initialize the locking parameters */
     memset(&f, 0, sizeof(f));
@@ -4186,36 +4181,44 @@ static int unixShmSystemLock(
 
   /* Update the global lock state and do debug tracing */
 #ifdef SQLITE_DEBUG
-  { u16 mask;
-  OSTRACE(("SHM-LOCK "));
-  mask = ofst>31 ? 0xffff : (1<<(ofst+n)) - (1<<ofst);
-  if( rc==SQLITE_OK ){
-    if( lockType==F_UNLCK ){
-      OSTRACE(("unlock %d ok", ofst));
-      pShmNode->exclMask &= ~mask;
-      pShmNode->sharedMask &= ~mask;
-    }else if( lockType==F_RDLCK ){
-      OSTRACE(("read-lock %d ok", ofst));
-      pShmNode->exclMask &= ~mask;
-      pShmNode->sharedMask |= mask;
-    }else{
-      assert( lockType==F_WRLCK );
-      OSTRACE(("write-lock %d ok", ofst));
-      pShmNode->exclMask |= mask;
-      pShmNode->sharedMask &= ~mask;
-    }
-  }else{
-    if( lockType==F_UNLCK ){
-      OSTRACE(("unlock %d failed", ofst));
-    }else if( lockType==F_RDLCK ){
-      OSTRACE(("read-lock failed"));
+  if( ofst<UNIX_SHM_DMS ){
+    u16 mask;
+
+    /* Shared locks never span more than one byte */
+    assert( n==1 || lockType!=F_RDLCK );
+
+    /* Locks are within range */
+    assert( n>=1 && n<=SQLITE_SHM_NLOCK );
+
+    OSTRACE(("SHM-LOCK "));
+    mask = ofst>31 ? 0xffff : (1<<(ofst+n)) - (1<<ofst);
+    if( rc==SQLITE_OK ){
+      if( lockType==F_UNLCK ){
+        OSTRACE(("unlock %d ok", ofst));
+        pShmNode->exclMask &= ~mask;
+        pShmNode->sharedMask &= ~mask;
+      }else if( lockType==F_RDLCK ){
+        OSTRACE(("read-lock %d ok", ofst));
+        pShmNode->exclMask &= ~mask;
+        pShmNode->sharedMask |= mask;
+      }else{
+        assert( lockType==F_WRLCK );
+        OSTRACE(("write-lock %d ok", ofst));
+        pShmNode->exclMask |= mask;
+        pShmNode->sharedMask &= ~mask;
+      }
     }else{
-      assert( lockType==F_WRLCK );
-      OSTRACE(("write-lock %d failed", ofst));
+      if( lockType==F_UNLCK ){
+        OSTRACE(("unlock %d failed", ofst));
+      }else if( lockType==F_RDLCK ){
+        OSTRACE(("read-lock failed"));
+      }else{
+        assert( lockType==F_WRLCK );
+        OSTRACE(("write-lock %d failed", ofst));
+      }
     }
-  }
-  OSTRACE((" - afterwards %03x,%03x\n",
-           pShmNode->sharedMask, pShmNode->exclMask));
+    OSTRACE((" - afterwards %03x,%03x\n",
+             pShmNode->sharedMask, pShmNode->exclMask));
   }
 #endif
 
@@ -4389,17 +4392,38 @@ static int unixOpenSharedMemory(unixFile *pDbFd){
       */
       robustFchown(pShmNode->h, sStat.st_uid, sStat.st_gid);
   
-      /* Check to see if another process is holding the dead-man switch.
-      ** If not, truncate the file to zero length. 
+      /* Do not allow a read-only process to connect if there are no
+      ** writers, because a read-only process is unable to recover the
+      ** shm file following a system crash.
       */
       rc = SQLITE_OK;
+      if( pShmNode->isReadonly ){
+        if( !unixShmSystemLock(pDbFd, F_RDLCK, UNIX_SHM_DMS, UNIX_SHM_N_DMS) ){
+          rc = SQLITE_CANTOPEN_DIRTYWAL;
+        }
+      }
+
+      /* If we are able to grab the dead-man switch, that means this is the
+      ** first (write-enable) process to connect to the database.  In that
+      ** case, truncate the shm file because the contents found on disk might
+      ** be invalid leftovers from a system crash.  The shm will be rebuilt
+      */
       if( unixShmSystemLock(pDbFd, F_WRLCK, UNIX_SHM_DMS, 1)==SQLITE_OK ){
         if( robust_ftruncate(pShmNode->h, 0) ){
           rc = unixLogError(SQLITE_IOERR_SHMOPEN, "ftruncate", zShmFilename);
         }
       }
+
+      /* Acquires locks to tell other processes that a this process is
+      ** running and therefore the shm is valid they do not need to run
+      ** recovery.
+      */
       if( rc==SQLITE_OK ){
+        unsigned r;
         rc = unixShmSystemLock(pDbFd, F_RDLCK, UNIX_SHM_DMS, 1);
+        sqlite3_randomness(sizeof(r), &r);
+        r = 1 + (r%(UNIX_SHM_N_DMS-1));
+        (void)unixShmSystemLock(pDbFd, F_WRLCK, UNIX_SHM_DMS+r, 1);
       }
       if( rc ) goto shm_open_err;
     }

diff --git a/src/sqlite.h.in b/src/sqlite.h.in
index 9ff366304f201a3198c817924a6a10f4d695ee93..0c0ed25b309fb75480f89ff57b9ee4a69036622f 100644 (file)
--- a/src/sqlite.h.in
+++ b/src/sqlite.h.in
@@ -508,6 +508,7 @@ int sqlite3_exec(
 #define SQLITE_CANTOPEN_ISDIR          (SQLITE_CANTOPEN | (2<<8))
 #define SQLITE_CANTOPEN_FULLPATH       (SQLITE_CANTOPEN | (3<<8))
 #define SQLITE_CANTOPEN_CONVPATH       (SQLITE_CANTOPEN | (4<<8))
+#define SQLITE_CANTOPEN_DIRTYWAL       (SQLITE_CANTOPEN | (5<<8))
 #define SQLITE_CORRUPT_VTAB            (SQLITE_CORRUPT | (1<<8))
 #define SQLITE_READONLY_RECOVERY       (SQLITE_READONLY | (1<<8))
 #define SQLITE_READONLY_CANTLOCK       (SQLITE_READONLY | (2<<8))