Re: [LMDB] Lockups with robust mutexes and crashing processes

[Marcos-David Dione <marcos-david.dione@amadeus.com>]

Marcos-David Dione/NCE/AMADEUS wrote on 24/11/2014 11:10:42:
>         Seen like that I'm not sure if there's
a defined behaviour 
> for that. I'll ask in the glibc and/or kernel MLs and I'll come 
> back with the answer. 

        and here's the
answer:

> On 11/24/2014 03:34 PM, Marcos Dione wrote:
> >         We found a situation
where a robust mutex cannot be recovered
> > from a stale lock and we're wondering if
it's simply an undefined
> > situation or  a bug in the kernel.
Attached you will find the sample
> > code, which is loosely based on a glibc's
test case.The gist of it is as
> > follows:
> > 
> > 1. we open a file.
> > 2. we mmap it and use that mem to store
a robust mutex.
> > 3. we lock the mutex.
> > 4. we munmap the file.
> > 5. we close the file.
> 
> Undefined behaviour.
> 
> This results in undefined behaviour since the
allocated storage for
> the mutex object has been lost. You need to keep
that storage around
> for the robust algorithms to work with. Without
any data you can't
> do anything.

        Full answer:

https://sourceware.org/ml/libc-help/2014-11/msg00035.html

--
Marcos Dione
Astek Sud-Est
R&D-SSP-DTA-TAE-TDS
for Amadeus SAS
T: +33 (4)4 9704 1727
marcos-david.dione@amadeus.com