commit e7d5980e2a7b091d973171144de04397204ebcd7

Author: Panu Matilainen <pmatilai@redhat.com>

Date:   Tue May 28 08:56:22 2013 +0300

    Serialize BDB environment open/close (RhBug:924417 etc)

    - Introduce Yet Another Broken Lock[*] to serialize BDB environment open:

      otherwise we can end up calling dbenv->failchk() while another process

      is just joining the environment, leading to transient "Thread died in..."

      DB_RUNRECOVER errors. Also prevents races on chrooted operations where

      we remove the entire environment on close.

    - This should also make it possible to handle at least some cases of

      real DB_RUNRECOVER errors by just nuking the environment but that's

      another topic...

      [*] YABL as this is nowhere near foolproof or sufficient for all

          the possible variants, but better than not having it...

    (cherry picked from commit ad874d60e3804f1bcd64f3510e1e2dfbf81456cd)

diff --git a/lib/backend/db3.c b/lib/backend/db3.c

index de8071b..9d385c6 100644

--- a/lib/backend/db3.c

+++ b/lib/backend/db3.c

@@ -57,10 +57,42 @@ static uint32_t db_envflags(DB * db)

     return eflags;

 }

+/*

+ * Try to acquire db environment open/close serialization lock.

+ * Return the open, locked fd on success, -1 on failure.

+ */

+static int serialize_env(const char *dbhome)

+{

+    char *lock_path = rstrscat(NULL, dbhome, "/.dbenv.lock", NULL);

+    mode_t oldmask = umask(022);

+    int fd = open(lock_path, (O_RDWR|O_CREAT), 0644);

+    umask(oldmask);

+

+    if (fd >= 0) {

+	int rc;

+	struct flock info;

+	memset(&info, 0, sizeof(info));

+	info.l_type = F_WRLCK;

+	info.l_whence = SEEK_SET;

+	do {

+	    rc = fcntl(fd, F_SETLKW, &info;;

+	} while (rc == -1 && errno == EINTR);

+	    

+	if (rc == -1) {

+	    close(fd);

+	    fd = -1;

+	}

+    }

+

+    free(lock_path);

+    return fd;

+}

+

 static int db_fini(rpmdb rdb, const char * dbhome)

 {

     DB_ENV * dbenv = rdb->db_dbenv;

     int rc;

+    int lockfd = -1;

     uint32_t eflags = 0;

     if (dbenv == NULL)

@@ -72,6 +104,9 @@ static int db_fini(rpmdb rdb, const char * dbhome)

     }

     (void) dbenv->get_open_flags(dbenv, &eflags);

+    if (!(eflags & DB_PRIVATE))

+	lockfd = serialize_env(dbhome);

+

     rc = dbenv->close(dbenv, 0);

     rc = dbapi_err(rdb, "dbenv->close", rc, _debug);

@@ -89,6 +124,10 @@ static int db_fini(rpmdb rdb, const char * dbhome)

 	rpmlog(RPMLOG_DEBUG, "removed  db environment %s\n", dbhome);

     }

+

+    if (lockfd >= 0)

+	close(lockfd);

+

     return rc;

 }

@@ -122,6 +161,7 @@ static int db_init(rpmdb rdb, const char * dbhome)

     DB_ENV *dbenv = NULL;

     int rc, xx;

     int retry_open = 2;

+    int lockfd = -1;

     struct dbConfig_s * cfg = &rdb->cfg;

     /* This is our setup, thou shall not have other setups before us */

     uint32_t eflags = (DB_CREATE|DB_INIT_MPOOL|DB_INIT_CDB);

@@ -176,6 +216,24 @@ static int db_init(rpmdb rdb, const char * dbhome)

     }

     /*

+     * Serialize shared environment open (and clock) via fcntl() lock.

+     * Otherwise we can end up calling dbenv->failchk() while another

+     * process is joining the environment, leading to transient

+     * DB_RUNRECOVER errors. Also prevents races wrt removing the

+     * environment (eg chrooted operation). Silently fall back to

+     * private environment on failure to allow non-privileged queries

+     * to "work", broken as it might be.

+     */

+    if (!(eflags & DB_PRIVATE)) {

+	lockfd = serialize_env(dbhome);

+	if (lockfd < 0) {

+	    eflags |= DB_PRIVATE;

+	    retry_open--;

+	    rpmlog(RPMLOG_DEBUG, "serialize failed, using private dbenv\n");

+	}

+    }

+

+    /*

      * Actually open the environment. Fall back to private environment

      * if we dont have permission to join/create shared environment or

      * system doesn't support it..

@@ -208,6 +266,8 @@ static int db_init(rpmdb rdb, const char * dbhome)

     rdb->db_dbenv = dbenv;

     rdb->db_opens = 1;

+    if (lockfd >= 0)

+	close(lockfd);

     return 0;

 errxit:

@@ -216,6 +276,8 @@ errxit:

 	xx = dbenv->close(dbenv, 0);

 	xx = dbapi_err(rdb, "dbenv->close", xx, _debug);

     }

+    if (lockfd >= 0)

+	close(lockfd);

     return rc;

 }