Log Message:
-----------
Add a check to prevent overwriting valid data if smgrnblocks() gives a
wrong answer, as has been seen to occur with a buggy Linux kernel. Not
really our bug, but it's a simple test in a seldom-used control path,
so might as well have a defense.
Modified Files:
--------------
pgsql/src/backend/storage/buffer:
bufmgr.c (r1.210 -> r1.211)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/storage/buffer/bufmgr.c.diff?r1=1.210&r2=1.211)