Re: [9fans] Lock loop in malloc()

[Lucio De Re <lucio@proxima.alt.za>]

On Mon, Jul 25, 2011 at 10:42:11AM -0400, Russ Cox wrote:
>
> > However, it does not seem to be Bison that's at fault: it seems that an
> > invocation of alloc() tries to set a lock and never succeeds or gives up.
>
> It's possible that you've found a latent bug in malloc.
> However, that malloc has been running along pretty
> steadily for a decade at this point, so it wouldn't be
> my first guess.  My first guess would be that something
> in Bison or in the code you added has corrupted memory,
> so that the lock has been overwritten with garbage and
> therefore cannot be acquired.
>
Well, there has to be a problem, I agree that malloc() is used too
extensively in Plan 9 to only reveal a fault at this time.  The same may
be said of cpp, but it's more likely that something evil has been lurking
in there.  I really hope that it is not something I have done that causes
the problem, but I really can't see how that would be possible without
cpp's cooperation.

> The address passed to lock - 0x1f2f8 in the trace -
> should be the address of the symbol sbrkmempriv.
> I assume it will be, but check (if not, there's other
> memory corruption).  Assuming it is, that's in the bss
> so the most likely culprits for corruption are the
> symbols near it: run nm | sort and look around.
>
Following Erik's direction, it seems that the lock value is 0x0deadead,
so I will start with the premise that a problem has been detected, but
not fatally.  I'll need to dig into cpp, then.  Are there known limits
in cpp's input sizes?

> Another thing to do would be to take the bison code
> you are compiling to a Linux box and run it under
> valgrind.
>
I have heard good reports regarding valgrind, but it is totally foreign
to me, I'lll resort to that when I have no alternative left.  Thanks for
the advice, please forgive me for not following it immediately.

++L