Horton

Re: introduce dynamic shared memory registry

Tom Lane <tgl@sss.pgh.pa.us>

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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Nathan Bossart <nathandbossart@gmail.com>
Cc: Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com>, Abhijit Menon-Sen <ams@toroid.org>, Michael Paquier <michael@paquier.xyz>, Robert Haas <robertmhaas@gmail.com>, pgsql-hackers@postgresql.org
Date: 2024-01-21T16:21:46Z
Lists: pgsql-hackers 
Nathan Bossart <nathandbossart@gmail.com> writes:
> Committed.  Thanks everyone for reviewing!

Coverity complained about this:

*** CID 1586660:  Null pointer dereferences  (NULL_RETURNS)
/srv/coverity/git/pgsql-git/postgresql/src/backend/storage/ipc/dsm_registry.c: 185 in GetNamedDSMSegment()
179     	}
180     	else if (!dsm_find_mapping(entry->handle))
181     	{
182     		/* Attach to existing segment. */
183     		dsm_segment *seg = dsm_attach(entry->handle);
184     
>>>     CID 1586660:  Null pointer dereferences  (NULL_RETURNS)
>>>     Dereferencing a pointer that might be "NULL" "seg" when calling "dsm_pin_mapping".
185     		dsm_pin_mapping(seg);
186     		ret = dsm_segment_address(seg);
187     	}
188     	else
189     	{
190     		/* Return address of an already-attached segment. */

I think it's right --- the comments for dsm_attach explicitly
point out that a NULL return is possible.  You need to handle
that scenario in some way other than SIGSEGV.

			regards, tom lane

Commits

  1. Fix possible NULL pointer dereference in GetNamedDSMSegment().

  2. Teach autoprewarm to use the dynamic shared memory registry.

  3. Introduce the dynamic shared memory registry.

  4. doc: Reorganize section for shared memory and LWLocks.