Horton

Re: Using WaitEventSet in the postmaster

Andres Freund <andres@anarazel.de>

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From: Andres Freund <andres@anarazel.de>
To: Thomas Munro <thomas.munro@gmail.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2023-01-12T18:26:29Z
Lists: pgsql-hackers 
Hi,

On 2023-01-12 20:35:43 +1300, Thomas Munro wrote:
> Subject: [PATCH] Fix WaitEventSetWait() buffer overrun.
> 
> The WAIT_USE_EPOLL and WAIT_USE_KQUEUE implementations of
> WaitEventSetWaitBlock() confused the size of their internal buffer with
> the size of the caller's output buffer, and could ask the kernel for too
> many events.  In fact the set of events retrieved from the kernel needs
> to be able to fit in both buffers, so take the minimum of the two.
> 
> The WAIT_USE_POLL and WAIT_USE WIN32 implementations didn't have this
> confusion.

> This probably didn't come up before because we always used the same
> number in both places, but commit 7389aad6 calculates a dynamic size at
> construction time, while using MAXLISTEN for its output event buffer on
> the stack.  That seems like a reasonable thing to want to do, so
> consider this to be a pre-existing bug worth fixing.

> As reported by skink, valgrind and Tom Lane.
> 
> Discussion: https://postgr.es/m/901504.1673504836%40sss.pgh.pa.us

Makes sense. We should backpatch this, I think?

Greetings,

Andres Freund

Commits

  1. Remove unneeded volatile qualifiers from postmaster.c.

  2. Fix WaitEventSetWait() buffer overrun.

  3. Refactor DetermineSleepTime() to use milliseconds.

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

  5. Allow parent's WaitEventSets to be freed after fork().

  6. Don't leak a signalfd when using latches in the postmaster.

  7. Add WL_SOCKET_ACCEPT event to WaitEventSet API.

  8. From: Phil Thompson <phil@river-bank.demon.co.uk>