From: | Andres Freund <andres(at)anarazel(dot)de> |
---|---|
To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | Heikki Linnakangas <heikki(dot)linnakangas(at)iki(dot)fi>, pgsql-committers(at)lists(dot)postgresql(dot)org |
Subject: | Re: pgsql: Fix double-release of spinlock |
Date: | 2024-07-29 16:18:46 |
Message-ID: | 20240729161846.kgiafbe2dtgabxgb@awork3.anarazel.de |
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Hi,
On 2024-07-29 11:31:56 -0400, Tom Lane wrote:
> Heikki Linnakangas <heikki(dot)linnakangas(at)iki(dot)fi> writes:
> > Commit 9d9b9d46f3 added spinlocks to protect the fields in ProcSignal
> > flags, but in EmitProcSignalBarrier(), the spinlock was released
> > twice. With most spinlock implementations, releasing a lock that's not
> > held is not easy to notice, because most of the time it does nothing,
> > but if the spinlock was concurrently acquired by another process, it
> > could lead to more serious issues. Fortunately, with the
> > --disable-spinlocks emulation implementation, it caused more visible
> > failures.
>
> There was some recent discussion about getting rid of
> --disable-spinlocks on the grounds that nobody would use
> hardware that lacked native spinlocks. But now I wonder
> if there is a testing/debugging reason to keep it.
Seems it'd be a lot more straightforward to just add an assertion to the
x86-64 spinlock implementation verifying that the spinlock isn't already free?
Greetings,
Andres Freund
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