Re: kern/29360: vfs.generic.usermount and mount(8) general questions

[Antti Kantee <pooka%cs.hut.fi@localhost>]

The following reply was made to PR kern/29360; it has been noted by GNATS.

From: Antti Kantee <pooka%cs.hut.fi@localhost>
To: Manuel Bouyer <bouyer%antioche.eu.org@localhost>
Cc: Elad Efrat <elad%NetBSD.org@localhost>, gnats-bugs%NetBSD.org@localhost,
        tech-kern%NetBSD.org@localhost
Subject: Re: kern/29360: vfs.generic.usermount and mount(8) general questions
Date: Sun, 6 Sep 2009 21:23:19 +0300

 On Sun Sep 06 2009 at 17:24:56 +0200, Manuel Bouyer wrote:
 > > As I recall, it was
 > > added because mounting enough file systems (I used kernfs for testing back
 > > then) would cause the kernel to run out of memory and the system to panic.
 > 
 > I think the discussion about this also refereced the above SA (which had been
 > fixed at this time, but showed how fragile usermounts are), but I may
 > be wrong.
 
 Apparently you can still make the system panic by just mounting a zillion
 kernfs's (which is just one way to make the kernel run out of memory).
 I think the problem is that somewhere along the line kmem_alloc(KM_SLEEP)
 returns NULL.  I remember there being discussions that the caller of
 kmem_alloc() should always check against NULL return, but that of course
 makes calling it slightly inconvenient.