Re: kern/55402: amd64/9.99.68/9.99.68: xen/zfs - kernel: double fault trap, code=0

[Jaromír Doleček <jaromir.dolecek%gmail.com@localhost>]

The following reply was made to PR kern/55402; it has been noted by GNATS.

From: =?UTF-8?B?SmFyb23DrXIgRG9sZcSNZWs=?= <jaromir.dolecek%gmail.com@localhost>
To: Frank Kardel <kardel%netbsd.org@localhost>
Cc: "gnats-bugs%NetBSD.org@localhost" <gnats-bugs%netbsd.org@localhost>
Subject: Re: kern/55402: amd64/9.99.68/9.99.68: xen/zfs - kernel: double fault
 trap, code=0
Date: Sat, 20 Jun 2020 21:57:44 +0200

 Le sam. 20 juin 2020 =C3=A0 21:00, Frank Kardel <kardel%netbsd.org@localhost> a =C3=
 =A9crit :
 > I do have the feeling that zfs code is very generous with stack. Also
 > scan has a recursive structure where I don't know the upper bound
 
 Both Linux and FreeBSD have the same kernel stack size as we do on
 amd64 - 16KB, i.e. 4 pages.
 
 It however seems that _something_ blows up when stack overflows the
 3rd page already, i.e. around 12288 bytes mark. I'll investigate this
 separately.
 
 I checked FreeBSD code, they have some changes in dsl_scan.c which as
 a side effect reduced the stack usage on the dsl_scan_*() recursion. Maybe
 that is the reason why it works there.
 
 Anyway, it seems both changes are necessary, so I'll eventually commit
 them. Thanks for testing.
 
 Jaromir