Horton

Re: Refactoring backend fork+exec code

Thomas Munro <thomas.munro@gmail.com>

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From: Thomas Munro <thomas.munro@gmail.com>
To: Heikki Linnakangas <hlinnaka@iki.fi>
Cc: pgsql-hackers <pgsql-hackers@postgresql.org>, reid.thompson@crunchydata.com, Robert Haas <robertmhaas@gmail.com>, Andres Freund <andres@anarazel.de>, Tristan Partin <tristan@neon.tech>
Date: 2024-05-18T05:24:45Z
Lists: pgsql-hackers

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. Avoid 0-length memcpy to NULL with EXEC_BACKEND

  2. Tighten check for --forkchild argument when spawning child process

  3. Add missing PGDLLIMPORT markings

  4. Remove assertions that some compiler say are tautological

  5. Move code for backend startup to separate file

  6. Refactor postmaster child process launching

  7. Move some functions from postmaster.c to a new source file

  8. Split registration of Win32 deadchild callback to separate function

  9. Improve log messages referring to background worker processes

  10. Move initialization of the Port struct to the child process

  11. Pass CAC as an argument to the backend process

  12. Set socket options in child process after forking

  13. Fix references to renamed function in comments

  14. Use MyBackendType in more places to check what process this is

  15. Remove MyAuxProcType, use MyBackendType instead

  16. Replace BackendIds with 0-based ProcNumbers

  17. Redefine backend ID to be an index into the proc array

  18. Remove superfluous 'pgprocno' field from PGPROC

  19. Fix incorrect comment on how BackendStatusArray is indexed

  20. Refactor how InitProcess is called

  21. Pass BackgroundWorker entry in the parameter file in EXEC_BACKEND mode

  22. Refactor CreateSharedMemoryAndSemaphores

  23. Silence Valgrind complaint with EXEC_BACKEND

  24. Adjust obsolete comment explaining set_stack_base().

  25. Print lwlock stats also for aux processes, when built with LWLOCK_STATS

  26. Move canAcceptConnections check from ProcessStartupPacket to caller.

  27. Fix crash on syslogger startup

  28. Refactor ListenSocket array.

  29. Use FD_CLOEXEC on ListenSockets

  30. Don't leak descriptors into subprograms.

  31. Use WaitEventSet API for postmaster's event loop.

  32. Rearrange postmaster's startup sequence for better syslogger results.

  33. Fix and enhance the assertion of no palloc's in a critical section.

On Mon, Mar 18, 2024 at 10:41 PM Heikki Linnakangas <hlinnaka@iki.fi> wrote:
> Committed, with some final cosmetic cleanups. Thanks everyone!

Nitpicking from UBSan with EXEC_BACKEND on Linux (line numbers may be
a bit off, from a branch of mine):

../src/backend/postmaster/launch_backend.c:772:2: runtime error: null
pointer passed as argument 2, which is declared to never be null
==13303==Using libbacktrace symbolizer.
    #0 0x5555564b0202 in save_backend_variables
../src/backend/postmaster/launch_backend.c:772
    #1 0x5555564b0242 in internal_forkexec
../src/backend/postmaster/launch_backend.c:311
    #2 0x5555564b0bdd in postmaster_child_launch
../src/backend/postmaster/launch_backend.c:244
    #3 0x5555564b3121 in StartChildProcess
../src/backend/postmaster/postmaster.c:3928
    #4 0x5555564b933a in PostmasterMain
../src/backend/postmaster/postmaster.c:1357
    #5 0x5555562de4ad in main ../src/backend/main/main.c:197
    #6 0x7ffff667ad09 in __libc_start_main
(/lib/x86_64-linux-gnu/libc.so.6+0x23d09)
    #7 0x555555e34279 in _start
(/tmp/cirrus-ci-build/build/tmp_install/usr/local/pgsql/bin/postgres+0x8e0279)

This silences it:

-       memcpy(param->startup_data, startup_data, startup_data_len);
+       if (startup_data_len > 0)
+               memcpy(param->startup_data, startup_data, startup_data_len);

(I found that out by testing EXEC_BACKEND on CI.  I also learned that
the Mac and FreeBSD tasks fail with EXEC_BACKEND because of SysV shmem
bleating.  We probably should go and crank up the relevant sysctls in
the .cirrus.tasks.yml...)