Date: Wed, 28 Jul 2021 16:01:01 -0400
From: Alvaro Herrera <alvherre@alvh.no-ip.org>
To: exclusion@gmail.com, pgsql-bugs@lists.postgresql.org
Subject: Re: BUG #17126: Server crashes on dropping user while enumerating
 owned objects that are droppped concurrently
Message-ID: <202107282001.rfd75lew2c33@alvherre.pgsql>
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On 2021-Jul-28, PG Bug reporting form wrote:

> Dropping a user that owns a number of procedures, while some of them are
> being dropped, can cause the server crash:
> 
> Core was generated by `postgres: law regression [local] DROP ROLE           
>                         '.
> Program terminated with signal SIGABRT, Aborted.
> #0  __GI_raise (sig=sig@entry=6) at ../sysdeps/unix/sysv/linux/raise.c:50
> 50      ../sysdeps/unix/sysv/linux/raise.c: No such file or directory.
> (gdb) bt
> #0  __GI_raise (sig=sig@entry=6) at ../sysdeps/unix/sysv/linux/raise.c:50
> #1  0x00007f268882b859 in __GI_abort () at abort.c:79
> #2  0x000055a23a628276 in ExceptionalCondition (conditionName=conditionName@entry=0x55a23a77fd4d "pointer != NULL", 
>     errorType=errorType@entry=0x55a23a68700b "FailedAssertion", fileName=0x7ffdf4459470 "W\202b:\242U", 
>     fileName@entry=0x55a23a7886b0 "../../../../src/include/utils/memutils.h", lineNumber=lineNumber@entry=123)
>     at assert.c:69
> #3  0x000055a23a65b46e in GetMemoryChunkContext (pointer=0x0) at ../../../../src/include/utils/memutils.h:123
> #4  pfree (pointer=pointer@entry=0x0) at mcxt.c:1171
> #5  0x000055a23a23254f in storeObjectDescription (descs=descs@entry=0x7ffdf44598b0, type=LOCAL_OBJECT, 
>     object=object@entry=0x55a23b5efe10, deptype=SHARED_DEPENDENCY_OWNER, count=count@entry=0) at pg_shdepend.c:1267

There's many places that deal correctly with the possibility that
getObjectDescription() would return NULL, but I found two places that
don't.

-- 
Álvaro Herrera         PostgreSQL Developer  —  https://www.EnterpriseDB.com/

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diff --git a/src/backend/catalog/dependency.c b/src/backend/catalog/dependency.c
index 76b65e39c4..d9a00aab85 100644
--- a/src/backend/catalog/dependency.c
+++ b/src/backend/catalog/dependency.c
@@ -1092,6 +1092,10 @@ reportDependentObjects(const ObjectAddresses *targetObjects,
 
 		objDesc = getObjectDescription(obj, false);
 
+		/* An object being dropped concurrently doesn't need to be reported */
+		if (objDesc == NULL)
+			continue;
+
 		/*
 		 * If, at any stage of the recursive search, we reached the object via
 		 * an AUTO, INTERNAL, PARTITION, or EXTENSION dependency, then it's
diff --git a/src/backend/catalog/pg_shdepend.c b/src/backend/catalog/pg_shdepend.c
index 4b676f5607..e9bf16af3e 100644
--- a/src/backend/catalog/pg_shdepend.c
+++ b/src/backend/catalog/pg_shdepend.c
@@ -1231,6 +1231,12 @@ storeObjectDescription(StringInfo descs,
 {
 	char	   *objdesc = getObjectDescription(object, false);
 
+	/*
+	 * An object being dropped concurrently doesn't need to be reported.
+	 */
+	if (objdesc == NULL)
+		return;
+
 	/* separate entries with a newline */
 	if (descs->len != 0)
 		appendStringInfoChar(descs, '\n');

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