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Date: Tue, 29 Sep 2020 14:48:05 -0400
From: Rich Felker <dalias@...c.org>
To: Leonid Shamis <leonid.shamis@...il.com>
Cc: musl@...ts.openwall.com
Subject: Re: Robust mutex returning ESRCH
On Tue, Sep 29, 2020 at 09:31:12AM -0700, Leonid Shamis wrote:
> We had a bug in our code where a dying process released shared memory
> (munmap) prior to exit. The process held ownership of a robust mutex within
> the shared memory, and because the address was unmapped, the robust_list
> wasn't able to set the appropriate flags.
>
> The next attempt to lock the mutex, in another process, returned ESRCH.
>
> Should ESRCH be caughtand converted to either a recoverable EOWNERDEAD or
> ENOTRECOVERABLE?
Was it also priority-inheritance? Otherwise I don't see where ESRCH
should have come from. Unmapping the mutex while you hold is should
almost surely be treated as undefined (though I don't think the
standard spells this out explicitly anywhere). It probably would be
nice to avoid returning a bogus error code to the non-erroneous caller
sharing the robust mutex with a program that has UB, but I don't think
Linux admits any efficient general solution here.
Rich
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