[Bug 282994] Repeated kernel panics

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=282994

Mark Johnston <markj@FreeBSD.org> changed:

           What    |Removed                     |Added
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             Status|New                         |Open
                 CC|                            |markj@FreeBSD.org

--- Comment #3 from Mark Johnston <markj@FreeBSD.org> ---
> 5. They all use RCTL to control resources used by users.

The problem is that shm_alloc() assumes that object allocation won't fail, but
this is false:
- racct rules which restrict swap usage can cause swap_reserve_by_cred() to
fail;
- some overcommit modes limit swap reservations such that
swap_reserve_by_cred() can fail.

I suspect that changing your racct rules will work around the problem. 
RACCT_SWAP works by limiting the maximum number and size of swap-backed
objects, rather than swap device usage.  In particular, it treats swap object
allocation as a "reservation" and that counts against the limit before swap
space is actually used.  I'm a bit skeptical that this implementation is very
useful.

I wrote a patch which prevents the crash, but note that you'll get shm object
allocation failures instead, which might cause all kinds of problems:
https://reviews.freebsd.org/D47839

(In reply to jSML4ThWwBID69YC from comment #1)
Changing your racct rules might address these problems as well.

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