Teach DSM registry to ERROR if attaching to an uninitialized entry.

If DSM entry initialization fails, backends could try to use an
uninitialized DSM segment, DSA, or dshash table (since the entry is
still added to the registry).  To fix, keep track of whether
initialization completed, and ERROR if a backend tries to attach to
an uninitialized entry.  We could instead retry initialization as
needed, but that seemed complicated, error prone, and unlikely to
help most cases.  Furthermore, such problems probably indicate a
coding error.

Reported-by: Alexander Lakhin <exclusion@gmail.com>
Reviewed-by: Sami Imseih <samimseih@gmail.com>
Discussion: https://postgr.es/m/dd36d384-55df-4fc2-825c-5bc56c950fa9%40gmail.com
Backpatch-through: 17

diff --git a/src/backend/storage/ipc/dsm_registry.c b/src/backend/storage/ipc/dsm_registry.c
index 1d4fd31ffedbc4b6342b5189fdd3244fd89cc170..8511b7afc7bb4d72ae631eccdff2822eb3953494 100644 (file)
--- a/src/backend/storage/ipc/dsm_registry.c
+++ b/src/backend/storage/ipc/dsm_registry.c
@@ -45,6 +45,7 @@ typedef struct DSMRegistryEntry
    char        name[64];
    dsm_handle  handle;
    size_t      size;
+   bool        initialized;
 } DSMRegistryEntry;
 
 static const dshash_parameters dsh_params = {
@@ -158,8 +159,12 @@ GetNamedDSMSegment(const char *name, size_t size,
    entry = dshash_find_or_insert(dsm_registry_table, name, found);
    if (!(*found))
    {
+       dsm_segment *seg;
+
+       entry->initialized = false;
+
        /* Initialize the segment. */
-       dsm_segment *seg = dsm_create(size, 0);
+       seg = dsm_create(size, 0);
 
        dsm_pin_segment(seg);
        dsm_pin_mapping(seg);
@@ -169,13 +174,17 @@ GetNamedDSMSegment(const char *name, size_t size,
 
        if (init_callback)
            (*init_callback) (ret);
+
+       entry->initialized = true;
    }
+   else if (!entry->initialized)
+       ereport(ERROR,
+               (errmsg("requested DSM segment \"%s\" failed initialization",
+                       name)));
    else if (entry->size != size)
-   {
        ereport(ERROR,
-               (errmsg("requested DSM segment size does not match size of "
-                       "existing segment")));
-   }
+               (errmsg("requested DSM segment \"%s\" does not match size of existing entry",
+                       name)));
    else
    {
        dsm_segment *seg = dsm_find_mapping(entry->handle);