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Tom Lane 2569ca0dc8 Fix longstanding recursion hazard in sinval message processing. 
LockRelationOid and sibling routines supposed that, if our session already
holds the lock they were asked to acquire, they could skip calling
AcceptInvalidationMessages on the grounds that we must have already read
any remote sinval messages issued against the relation being locked.
This is normally true, but there's a critical special case where it's not:
processing inside AcceptInvalidationMessages might attempt to access system
relations, resulting in a recursive call to acquire a relation lock.

Hence, if the outer call had acquired that same system catalog lock, we'd
fall through, despite the possibility that there's an as-yet-unread sinval
message for that system catalog.  This could, for example, result in
failure to access a system catalog or index that had just been processed
by VACUUM FULL.  This is the explanation for buildfarm failures we've been
seeing intermittently for the past three months.  The bug is far older
than that, but commits a54e1f158 et al added a new recursion case within
AcceptInvalidationMessages that is apparently easier to hit than any
previous case.

To fix this, we must not skip calling AcceptInvalidationMessages until
we have *finished* a call to it since acquiring a relation lock, not
merely acquired the lock.  (There's already adequate logic inside
AcceptInvalidationMessages to deal with being called recursively.)
Fortunately, we can implement that at trivial cost, by adding a flag
to LOCALLOCK hashtable entries that tracks whether we know we have
completed such a call.

There is an API hazard added by this patch for external callers of
LockAcquire: if anything is testing for LOCKACQUIRE_ALREADY_HELD,
it might be fooled by the new return code LOCKACQUIRE_ALREADY_CLEAR
into thinking the lock wasn't already held.  This should be a fail-soft
condition, though, unless something very bizarre is being done in
response to the test.

Also, I added an additional output argument to LockAcquireExtended,
assuming that that probably isn't called by any outside code given
the very limited usefulness of its additional functionality.

Back-patch to all supported branches.

Discussion: https://postgr.es/m/12259.1532117714@sss.pgh.pa.us
2018-09-07 18:04:55 -04:00
config LLVMJIT: LLVMGetHostCPUFeatures now is upstream, use LLMV version if available. 2018-08-24 10:21:48 -07:00
contrib Make contrib/unaccent's unaccent() function work when not in search path. 2018-09-06 10:49:45 -04:00
doc Refactor installation of extension headers. 2018-09-07 14:30:15 +01:00
src Fix longstanding recursion hazard in sinval message processing. 2018-09-07 18:04:55 -04:00
.dir-locals.el Update documentation editor setup instructions 2018-07-13 21:28:18 +02:00
.gitattributes Remove contrib/tsearch2. 2017-02-13 11:06:11 -05:00
.gitignore Support for optimizing and emitting code in LLVM JIT provider. 2018-03-22 11:05:22 -07:00
aclocal.m4 Add configure infrastructure (--with-llvm) to enable LLVM support. 2018-03-20 17:26:25 -07:00
configure LLVMJIT: LLVMGetHostCPUFeatures now is upstream, use LLMV version if available. 2018-08-24 10:21:48 -07:00
configure.in Stamp 11beta3. 2018-08-06 16:02:42 -04:00
COPYRIGHT Update copyright for 2018 2018-01-02 23:30:12 -05:00
GNUmakefile.in Ensure we build generated headers at the start of some more cases. 2018-07-30 18:04:39 -04:00
HISTORY Change documentation references to PG website to use https: not http: 2017-05-20 21:50:47 -04:00
Makefile Fix non-GNU makefiles for AIX make. 2017-11-30 00:57:22 -08:00
README Change documentation references to PG website to use https: not http: 2017-05-20 21:50:47 -04:00
README.git Change documentation references to PG website to use https: not http: 2017-05-20 21:50:47 -04:00

README 

PostgreSQL Database Management System
=====================================

This directory contains the source code distribution of the PostgreSQL
database management system.

PostgreSQL is an advanced object-relational database management system
that supports an extended subset of the SQL standard, including
transactions, foreign keys, subqueries, triggers, user-defined types
and functions.  This distribution also contains C language bindings.

PostgreSQL has many language interfaces, many of which are listed here:

	https://www.postgresql.org/download

See the file INSTALL for instructions on how to build and install
PostgreSQL.  That file also lists supported operating systems and
hardware platforms and contains information regarding any other
software packages that are required to build or run the PostgreSQL
system.  Copyright and license information can be found in the
file COPYRIGHT.  A comprehensive documentation set is included in this
distribution; it can be read as described in the installation
instructions.

The latest version of this software may be obtained at
https://www.postgresql.org/download/.  For more information look at our
web site located at https://www.postgresql.org/.