svn commit: r286223 - head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs

[Steven Hartland]

On 03/08/2015 12:19, Konstantin Belousov wrote:
> On Mon, Aug 03, 2015 at 03:52:21AM -0700, Peter Wemm wrote:
>> On Monday, August 03, 2015 11:31:58 AM Steven Hartland wrote:
>>> On 03/08/2015 10:47, Slawa Olhovchenkov wrote:
>>>> On Mon, Aug 03, 2015 at 09:34:10AM +0000, Steven Hartland wrote:
>>>>> Author: smh
>>>>> Date: Mon Aug  3 09:34:09 2015
>>>>> New Revision: 286223
>>>>> URL: https://svnweb.freebsd.org/changeset/base/286223
>>>>>
>>>>> Log:
>>>>>     Fix KSTACK_PAGES check in ZFS module
>>>>>     
>>>>>     The check introduced by r285946 failed to add the dependency on
>>>>>     opt_kstack_pages.h which meant the default value for the platform
>>>>>     instead
>>>>>     of the customised options KSTACK_PAGES=X was being tested.
>>>>>     
>>>>>     Also wrap in #ifdef __FreeBSD__ for portability.
>>>> /usr/src/sys/kern/kern_proc.c:int kstack_pages = KSTACK_PAGES;
>>>>
>>>> May be check variable kstack_pages is best way?
>>>> Eliminate dependency on foreign opt_XXXX.
>>> I did think of that but as other modules such as dtrace, which is also
>>> cddl code, already have this dependency I went with this.
>>>
>>> I'm easy though, if there's a concusses that kstack_pages or possibly
>>> curthread->td_kstack_pages, which would take into account the
>>> possibility of varied thread stack sizes, then I can make that change.
>>>
>>> What do others think?
>> The whole thing has missing the point.
>>
>> Changing the default for the entire kernel just because the zfs compat
>> wrappers can't be bothered requesting a suitable value is.. unfortunate..
>> particularly when it is in freebsd-provided code, not upstream zfs code.
>>
>> Fix the kproc_kthread_add() calls in do_thread_create() and zvol_geom_run()
>> instead.  Enforce a lower bound there for zfs threads instead of making the
>> entire rest of the kernel use more memory.
>>
>> eg: I'm thinking along these lines:
>> Index: cddl/compat/opensolaris/sys/proc.h
>> ====================================================
>> --- cddl/compat/opensolaris/sys/proc.h	(revision 286224)
>> +++ cddl/compat/opensolaris/sys/proc.h	(working copy)
>> @@ -77,6 +77,8 @@
>>   	ASSERT(state == TS_RUN);
>>   	ASSERT(pp == &p0);
>>   
>> +	if (stksize < 16384)
>> +		stksize = 16384;	/* Enforce lower bound on ZFS threads */
>>   	error = kproc_kthread_add(proc, arg, &zfsproc, &td, RFSTOPPED,
>>   	    stksize / PAGE_SIZE, "zfskern", "solthread %p", proc);
>>   	if (error == 0) {
>>
>>
>> Beware, some platforms have large pages (eg: ia64 in -stable has 8k, 16k or
>> 32k pages, from memory).  Specifying an arbitrary number of pages in code
>> that's supposed to be portable isn't a good idea.
> This would not help. Issue is the size of the thread0 stack, which
> overflows in this case.
>
> I looked at the possibility of making default kernel stack size
> configurable by a loader tunable, and the issue is that thread0 gets its
> stack set up too early (locore for i386, hammer_time() for amd64).  I.e.,
> it is possible to make the setting effective for all threads after thread0,
> but not for the one which causes the issue.
>
> I do not want to modify ABI between loader and kernel to pass the parameter.
I've created a review for the current proposed change to look at the 
kernel var kstack_pages vs
the compile time define KSTACK_PAGES.

For this change I don't want to get into fixing the thread0 stack size, 
which can be done later, just
to provide a reasonable warning to the user that smaller values could 
cause a panic.

@slw I've added peter and kib as reviewers if you phabricator account 
then feel free to add yourself.

     Regards
     Steve