From: Tom Lane <tgl@sss.pgh.pa.us>
To: Andrew Dunstan <andrew@dunslane.net>
cc: PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Subject: Re: fix pg_mkdir_p to tolerate concurrent directory creation
In-reply-to: <3ca004de-e49b-4471-b8aa-fd656e70f68c@dunslane.net>
References: <3ca004de-e49b-4471-b8aa-fd656e70f68c@dunslane.net>
Comments: In-reply-to Andrew Dunstan <andrew@dunslane.net>
	message dated "Thu, 18 Jun 2026 09:18:37 -0400"
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Date: Thu, 18 Jun 2026 10:24:03 -0400
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Andrew Dunstan <andrew@dunslane.net> writes:
> While working on the pytest stuff, I found this issue when making it 
> work on Windows, but the issue can exist everywhere. pg_mkdir_p can fail 
> if there is a concurrent directory creation.

This bit:

+			if (errno != EEXIST || stat(path, &sb) != 0 || !S_ISDIR(sb.st_mode))
+			{
+				retval = -1;
+				break;
+			}

looks like it could corrupt the reported errno, ie stat() could
overwrite what mkdir() reported.

			regards, tom lane