Re: Deadlock in XLogInsert at AIX

Oh, you were one step ahead of me, I didn't understand it on first read
of your email. Need more coffee..

On 01/31/2017 05:03 PM, Konstantin Knizhnik wrote:
> I inspected code of pg_atomic_compare_exchange_u32_impl and didn't sync
> in prologue:
>
> (dbx) listi pg_atomic_compare_exchange_u32_impl
> [no sync instruction]

> and if I compile this fuctions standalone, I get the following assembler
> code:
>
> .pg_atomic_compare_exchange_u32_impl: # 0x0000000000000000 (H.4.NO_SYMBOL)
> stdu SP,-128(SP)
> std r3,176(SP)
> std r4,184(SP)
> std r5,192(SP)
> ld r0,192(SP)
> stw r0,192(SP)
> sync
> ld r4,176(SP)
> ld r3,184(SP)
> lwz r0,192(SP)
> extsw r0,r0
> lwa r5,0(r3)
> ...
>
> sync is here!

Ok, so, the 'sync' instruction gets lost somehow. That "standalone"
assemly version looks slightly different in other ways too, you perhaps
used different optimization levels, or it looks different when it's
inlined into the caller. Not sure which version of the function gdb
would show, when it's a "static inline" function. Would be good to check
the disassembly of LWLockAttemptLock(), to see if the 'sync' is there.

Certainly seems like a compiler bug, though.

- Heikki