svn commit: r192094 - head/sys/kern

[Florian Smeets]

On 15.05.09 12:38, Kostik Belousov wrote:
> On Fri, May 15, 2009 at 12:48:52PM +0300, Kostik Belousov wrote:
>> On Fri, May 15, 2009 at 10:06:13AM +0200, Peter Holm wrote:
>>> On Fri, May 15, 2009 at 09:02:39AM +0200, Ed Schouten wrote:
>>>> Hi Kostik,
>>>>
>>>> * Konstantin Belousov<kib at FreeBSD.org>  wrote:
>>>>> Log:
>>>>>    Do not advance req->oldidx when sysctl_old_user returning an
>>>>>    error due to copyout failure or short buffer.
>>>>>
>>>>>    The later breaks the usermode iterators of the sysctl results that pack
>>>>>    arbitrary number of variable-sized structures. Iterator expects that
>>>>>    kernel filled exactly oldlen bytes, and tries to interpret half-filled
>>>>>    or garbage structure at the end of the buffer. In particular,
>>>>>    kinfo_getfile(3) segfaulted.
>>>>>
>>>>>    Reported and tested by:	pho
>>>>>    MFC after:	3 weeks
>>>>
>>>> Is it possible that this change introduces a regression? Right now
>>>> `pstat -t' gets stuck in an infinite loop. I've added the following
>>>> printf:
>>>>
>>>> | Index: pstat.c
>>>> | ===================================================================
>>>> | --- pstat.c	(revision 192128)
>>>> | +++ pstat.c	(working copy)
>>>> | @@ -263,6 +263,7 @@
>>>> |  		if (errno != ENOMEM)
>>>> |  			err(1, "sysctlbyname()");
>>>> |  		len *= 2;
>>>> | +		printf("Going to %zu\n", len);
>>>> |  		if ((xttys = realloc(xttys, len)) == NULL)
>>>> |  			err(1, "realloc()");
>>>> |  	}
>>>>
>>>> pstat on -CURRENT prints:
>>>>
>>>> |       LINE   INQ  CAN  LIN  LOW  OUTQ  USE  LOW   COL  SESS  PGID STATE
>>>> | Going to 0
>>>> | Going to 0
>>>> | Going to 0
>>>> | ...
>>>>
>>>> If I use the same patch on RELENG_6, I get the expected result:
>>>>
>>>> |      LINE RAW CAN OUT IHIWT ILOWT OHWT LWT     COL STATE  SESS      PGID DISC
>>>> | Going to 272
>>>> | Going to 544
>>>> | Going to 1088
>>>> | Going to 2176
>>>> | Going to 4352
>>>> | Going to 8704
>>>> |   sysmouse  0   0   0     0     0    0   0       0 -             0     0 term
>>>> | ...
>>>>
>>>> So the problem is that sysctl overwrites the len argument with 0, even
>>>> if it returns back to userspace with ENOMEM.
>>>>
>>>> I see we have two changes in sysctl. In theory it could also be related
>>>> to jhb@'s changes to sysctl locking, but I suspect it's less likely.
>>>>
>>>
>>> I can confirm that it is r192094 that triggers the loop.
>>
>> Yes, this is what I mean when talked about a breakage.
>>
>> Below is the reversal of r192094 + the change to keep the old, ugly
>> behaviour of sysctl kern.proc.filedesc to return 0 on ENOMEM, but with
>> oldlen chopped at the end of the last completely written struct kern_info
>> instead of the middle of partially-written one.
>>
>> Peter, could you, please, retest ?
>
> Err, the patch.
>

[snip patch]

The patch fixes my problems.

Thanks,
Florian