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Re: greenfly lwlock corruption in REL_14_STABLE and REL_15_STABLE

From:	"Greg Burd" <greg(at)burd(dot)me>
To:	"Thomas Munro" <thomas(dot)munro(at)gmail(dot)com>
Cc:	pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>
Subject:	Re: greenfly lwlock corruption in REL_14_STABLE and REL_15_STABLE
Date:	2025-12-11 17:27:37
Message-ID:	4ccf62c4-48ed-47cb-badc-9ae436d91b39@app.fastmail.com
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On Wed, Dec 10, 2025, at 12:10 AM, Thomas Munro wrote:
> Beginning a week ago, greenfly (RISC-V, Clang 20.1) has failed like
> this in 5 of 8 runs of the pgbench tests on the two oldest branches:

Hey Thomas, raising this. I should more closely monitor my farm animals. As greenfly is one of them and my login name is littered in the logs (gburd) I suppose I should dive into this.

> TRAP: FailedAssertion("!(oldstate & LW_VAL_EXCLUSIVE)", File:
> "lwlock.c", Line: 1850, PID: 1536294)
> postgres: main: gburd postgres [local] CREATE
> TYPE(ExceptionalCondition+0x72)[0x2ad1326922]
> postgres: main: gburd postgres [local] CREATE
> TYPE(LWLockRelease+0x51e)[0x2ad1634e60]
> postgres: main: gburd postgres [local] CREATE
> TYPE(_bt_first+0x7f8)[0x2ad139c314]
> postgres: main: gburd postgres [local] CREATE
> TYPE(btgettuple+0xca)[0x2ad13996f8]
> postgres: main: gburd postgres [local] CREATE
> TYPE(index_getnext_tid+0x2a)[0x2ad138bd66]
> postgres: main: gburd postgres [local] CREATE
> TYPE(index_getnext_slot+0x24)[0x2ad138bf56]
> postgres: main: gburd postgres [local] CREATE
> TYPE(systable_getnext+0x18)[0x2ad138a97c]
> postgres: main: gburd postgres [local] CREATE
> TYPE(GetNewOidWithIndex+0xfc)[0x2ad13ed284]
> postgres: main: gburd postgres [local] CREATE
> TYPE(EnumValuesCreate+0x58)[0x2ad14090ec]
> postgres: main: gburd postgres [local] CREATE
> TYPE(DefineEnum+0x10a)[0x2ad14bb948]
> postgres: main: gburd postgres [local] CREATE TYPE(+0x3f0336)[0x2ad164a336]
> postgres: main: gburd postgres [local] CREATE
> TYPE(standard_ProcessUtility+0x468)[0x2ad1649560]
> postgres: main: gburd postgres [local] CREATE TYPE(+0x3eec0e)[0x2ad1648c0e]
> postgres: main: gburd postgres [local] CREATE TYPE(+0x3ee418)[0x2ad1648418]
> postgres: main: gburd postgres [local] CREATE
> TYPE(PortalRun+0x160)[0x2ad1647ec8]
> postgres: main: gburd postgres [local] CREATE
> TYPE(PostgresMain+0x1b34)[0x2ad1646000]
> postgres: main: gburd postgres [local] CREATE TYPE(+0x36205a)[0x2ad15bc05a]
> postgres: main: gburd postgres [local] CREATE
> TYPE(ClosePostmasterPorts+0x0)[0x2ad15bb8e0]
> postgres: main: gburd postgres [local] CREATE
> TYPE(PostmasterMain+0x100a)[0x2ad15b92ac]
> postgres: main: gburd postgres [local] CREATE TYPE(+0x2cac90)[0x2ad1524c90]
> /lib/riscv64-linux-gnu/libc.so.6(+0x277cc)[0x3f9caa77cc]
> /lib/riscv64-linux-gnu/libc.so.6(__libc_start_main+0x78)[0x3f9caa7878]
> postgres: main: gburd postgres [local] CREATE TYPE(_start+0x20)[0x2ad1326ac0]
>
> That's:
>
> if (mode == LW_EXCLUSIVE)
> oldstate = pg_atomic_sub_fetch_u32(&lock->state, LW_VAL_EXCLUSIVE);
> else
> oldstate = pg_atomic_sub_fetch_u32(&lock->state, LW_VAL_SHARED);
>
> /* nobody else can have that kind of lock */
> Assert(!(oldstate & LW_VAL_EXCLUSIVE));
>
> I will see if I can reproduce it or see something wrong under qemu,
> but that'll take some time to set up...

It'll take me far less time to reproduce than you. :)

I'll see what I can do to find the offending commit(s).

best.

-greg

In response to

greenfly lwlock corruption in REL_14_STABLE and REL_15_STABLE at 2025-12-10 05:10:20 from Thomas Munro

Responses

Re: greenfly lwlock corruption in REL_14_STABLE and REL_15_STABLE at 2025-12-12 00:54:52 from Thomas Munro

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