Date: Sun, 19 Mar 2017 20:52:50 +0000 From: Rick Macklem <rmacklem@uoguelph.ca> To: Konstantin Belousov <kostikbel@gmail.com> Cc: Dimitry Andric <dim@FreeBSD.org>, Ian Lepore <ian@FreeBSD.org>, "Gergely Czuczy" <gergely.czuczy@harmless.hu>, FreeBSD Current <freebsd-current@freebsd.org> Subject: Re: process killed: text file modification Message-ID: <YTXPR01MB0189F47B6A23C10BFE8A85E6DD3B0@YTXPR01MB0189.CANPRD01.PROD.OUTLOOK.COM> In-Reply-To: <20170318032150.GW16105@kib.kiev.ua> References: <5ac94b9a-7ced-9eff-d746-7dddaaeca516@harmless.hu> <1489340839.40576.82.camel@freebsd.org> <FF55DB37-4A6B-4D88-B201-B3BCA1A11E87@FreeBSD.org> <YTXPR01MB01898D49933A82170FCAB7A0DD390@YTXPR01MB0189.CANPRD01.PROD.OUTLOOK.COM> <YTXPR01MB018944EF4248402AD421D825DD390@YTXPR01MB0189.CANPRD01.PROD.OUTLOOK.COM> <20170317083605.GQ16105@kib.kiev.ua> <YTXPR01MB0189F7147A7C5C5F8C56B2F1DD390@YTXPR01MB0189.CANPRD01.PROD.OUTLOOK.COM> <20170317141917.GS16105@kib.kiev.ua> <D0770019-3EEA-45D2-A751-18DF1B274F90@FreeBSD.org> <YTXPR01MB0189FBB6CF664653C1162936DD390@YTXPR01MB0189.CANPRD01.PROD.OUTLOOK.COM>, <20170318032150.GW16105@kib.kiev.ua>
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Kostik wrote:
[stuff snipped]
>> >> Dirty pages are flushed by writes, so if we have a set of dirty pages=
and
>> >> async vm_object_page_clean() is called on the vnode' vm_object, we ge=
t
>> >> a bunch of delayed-write AKA dirty buffers. This is possible even af=
ter
>> >> VOP_CLOSE() was done, e.g. by syncer performing regular run involving
>> >> vfs_msync().
>> When I was talking about ncl_flush() above, I was referring to buffer ca=
che
>> buffers written by a write(2) syscall, not the case of mmap'd pages.
> But dirty buffers can appear on the vnode queue due to dirty pages msynci=
ng
> by syncer, for instance.
Ok, just to clarify this, in case I don't understand it...
- You aren't saying that anything will be added to v_bufobj.bo_dirty.bv_hd =
by
vfs_msync() or similar, after VOP_CLOSE(), right?
--> ncl_flush() { was called nfs_flush() in the old NFS client } only deals=
with
"struct buf's" hanging off v_bufobj.bo_dirty.bv_hd, so I don't see a u=
se for
it in the patch.
As for pages added to v_bufobj.bo_object...the patch assumes that the proce=
ss
that was writing the executable file mmap'd is done { normally exited } bef=
ore
the exec() syscall occurs. If it is still dirtying pages when the exec() oc=
curs, then
failing with "Text file modified" seems correct to me. As you mentioned, an=
other
client can do this to the file anyhow.
My understanding is that vm_object_page_clean() will get all the dirty page=
s written
back to the server at that point and if that is done in VOP_SET_TEXT() as t=
his patch
does, what more can the NFS client do?
[more stuff snipped]
> Syncer does not open the vnode inside the vfs_msync() operations.
Ok, but this doesn't put "struct buf's" on v_bufobj.bo_dirty.bv_hd. Am I ri=
ght?
(When I said "buffers". I meant "struct buf's" under bo_dirty, not stuff un=
der
v_bufobj.bo_object.)
> We do track writeability to the file, and do not allow execution if there=
is
> an active writer, be it a file descriptor opened for write, or a writeabl=
e
> mapping. And in reverse, if the file is executed (VV_TEXT is set), then
> we disallow opening the file for write.
Yes, and that was why I figured doing this in VOP_SET_TEXT(), just before
setting VV_TEXT, was the right place to do it.
[more stuff snipped]
>
> Thanks for testing the patch. Now, if others can test it...rick
>
Again, hopefully others (especially the original reporter) will be able to
test the patch, rick
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