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Re: [PATCH]fix VM_CAN_NONLINEAR check in sys_remap_file_pages

Previous thread: [PATCH] virtualization of sysv msg queues is incomplete by Kirill Korotaev on Monday, October 8, 2007 - 7:05 am. (1 message)

Next thread: [PATCH 1/3] V4L: w9968cf, remove bad usage of ERESTARTSYS by Jiri Slaby on Monday, October 8, 2007 - 8:33 am. (16 messages)
[view original message]
From: Yan Zheng <yanzheng@...>
To: <linux-fsdevel@...>, <linux-kernel@...>, <akpm@...>
Subject: [PATCH]fix VM_CAN_NONLINEAR check in sys_remap_file_pages
Date: Monday, October 8, 2007 - 7:45 am

Hi all


The test for VM_CAN_NONLINEAR always fails


Signed-off-by: Yan Zheng<yanzheng@21cn.com>

----

diff -ur linux-2.6.23-rc9/mm/fremap.c linux/mm/fremap.c

--- linux-2.6.23-rc9/mm/fremap.c	2007-10-07 15:03:33.000000000 +0800

+++ linux/mm/fremap.c	2007-10-08 19:33:44.000000000 +0800

@@ -160,7 +160,7 @@

 	if (vma->vm_private_data && !(vma->vm_flags & VM_NONLINEAR))

 		goto out;


-	if (!vma->vm_flags & VM_CAN_NONLINEAR)

+	if (!(vma->vm_flags & VM_CAN_NONLINEAR))

 		goto out;


 	if (end <= start || start < vma->vm_start || end > vma->vm_end)

-
[view original message]
From: Hugh Dickins <hugh@...>
To: Yan Zheng <yanzheng@...>
Cc: Nick Piggin <nickpiggin@...>, Miklos Szeredi <miklos@...>, <linux-fsdevel@...>, <linux-kernel@...>, <akpm@...>
Subject: Re: [PATCH]fix VM_CAN_NONLINEAR check in sys_remap_file_pages
Date: Monday, October 8, 2007 - 9:37 am

Good catch indeed.  Though I was puzzled how we do nonlinear at all,

until I realized it's "The test for not VM_CAN_NONLINEAR always fails".


It's not as serious as it appears, since code further down has been

added more recently to simulate nonlinear on non-RAM-backed filesystems,

instead of going the real nonlinear way; so most filesystems are now not

required to do what VM_CAN_NONLINEAR was put in to ensure they could do.


I'm confused as to where that leaves us: is this actually a fix that

needs to go into 2.6.23?  or will it suddenly disable a system call

which has been silently working fine on various filesystems which did

not add VM_CAN_NONLINEAR?  could we just rip out VM_CAN_NONLINEAR?

I hope Nick or Miklos is clearer on what the risks are.


(Apologies for all the "not"s and "non"s here, I'm embarrassed

after just criticizing Ingo's SCHED_NO_NO_OMIT_FRAME_POINTER!)


-
[view original message]
From: Nick Piggin <nickpiggin@...>
To: Hugh Dickins <hugh@...>
Cc: Yan Zheng <yanzheng@...>, Miklos Szeredi <miklos@...>, <linux-fsdevel@...>, <linux-kernel@...>, <akpm@...>
Subject: Re: [PATCH]fix VM_CAN_NONLINEAR check in sys_remap_file_pages
Date: Monday, October 8, 2007 - 2:47 am

Well, I think all filesystems can do VM_CAN_NONLINEAR anyway. Device


We probably should keep VM_CAN_NONLINEAR for the moment, I think.

But now that we have the fallback path, we _could_ use that instead of

failing. I doubt anybody will be using nonlinear mappings on anything but

regular files for the time being, but as a trivial fix, I think this probably

should go into 2.6.23.


Thanks for spotting this problem

-
[view original message]
From: Yan Zheng <yanzheng@...>
To: Hugh Dickins <hugh@...>
Cc: Nick Piggin <nickpiggin@...>, Miklos Szeredi <miklos@...>, <linux-fsdevel@...>, <linux-kernel@...>, <akpm@...>
Subject: Re: [PATCH]fix VM_CAN_NONLINEAR check in sys_remap_file_pages
Date: Monday, October 8, 2007 - 6:50 pm

Yes, I mean "The test for not VM_CAN_NONLINEAR always fails".  please

forgive my poor English.

-
[view original message]
From: Andrew Morton <akpm@...>
To: Yan Zheng <yanzheng@...>
Cc: <linux-fsdevel@...>, <linux-kernel@...>, <linux-mm@...>
Subject: Re: [PATCH]fix VM_CAN_NONLINEAR check in sys_remap_file_pages
Date: Monday, October 8, 2007 - 1:04 pm

Lovely.  From this we can deduce that nobody has run remap_file_pages() since

2.6.23-rc1 and that nobody (including the developer who made that change) ran it

while that change was in -mm.


I'm surprise that LTP doesn't have any remap_file_pages() tests.


Have you runtime tested this change?


Thanks.

-
[view original message]
From: Nick Piggin <nickpiggin@...>
To: Andrew Morton <akpm@...>
Cc: Yan Zheng <yanzheng@...>, <linux-fsdevel@...>, <linux-kernel@...>, <linux-mm@...>
Subject: Re: [PATCH]fix VM_CAN_NONLINEAR check in sys_remap_file_pages
Date: Monday, October 8, 2007 - 3:02 am

But you'd be wrong. remap_file_pages was tested both with my own tester

and Ingo's test program.


vm_flags != 0, !vm_flags = 0, 0 & x = 0, so the test always falls

through. Of course, what I _should_ have done is also test a driver which

does not have VM_CAN_NONLINEAR... but even I wouldn't rewrite half

the nonlinear mapping code without once testing it ;)


FWIW, Oracle (maybe the sole real user of this) has been testing it, which

I'm very happy about (rather than testing after 2.6.23 is released).

-
[view original message]
From: Randy Dunlap <randy.dunlap@...>
To: Andrew Morton <akpm@...>
Cc: Yan Zheng <yanzheng@...>, <linux-fsdevel@...>, <linux-kernel@...>, <linux-mm@...>
Subject: Re: [PATCH]fix VM_CAN_NONLINEAR check in sys_remap_file_pages
Date: Monday, October 8, 2007 - 1:28 pm

I've run rmap-test with -M (use remap_file_pages) and

remap-test from ext3-tools, but not remap_file_pages for some reason.


I'll now add remap_file_pages soon.

Maybe those other 2 tests aren't strong enough (?).

Or maybe they don't return a non-0 exit status even when they fail...


---

~Randy

-
[view original message]
From: Andrew Morton <akpm@...>
To: Randy Dunlap <randy.dunlap@...>
Cc: <yanzheng@...>, <linux-fsdevel@...>, <linux-kernel@...>, <linux-mm@...>, <ltp-list@...>
Subject: Re: [PATCH]fix VM_CAN_NONLINEAR check in sys_remap_file_pages
Date: Monday, October 8, 2007 - 1:51 pm

On Mon, 8 Oct 2007 10:28:43 -0700


Me either.  There are a few lying around the place which could be

integrated.


It would be good if LTP were to have some remap_file_pages() tests

(please).  As we see here, it is something which we can easily break, and

leave broken for some time.


-
[view original message]
From: Yan Zheng <yanzheng@...>
To: Andrew Morton <akpm@...>
Cc: Randy Dunlap <randy.dunlap@...>, <linux-fsdevel@...>, <linux-kernel@...>, <linux-mm@...>, <ltp-list@...>
Subject: Re: [PATCH]fix VM_CAN_NONLINEAR check in sys_remap_file_pages
Date: Monday, October 8, 2007 - 9:43 pm

I found it by review, only do test to check remap_file_pages works

when VM_CAN_NONLINEAR flags is set.

-
[view original message]
From: Nick Piggin <nickpiggin@...>
To: Andrew Morton <akpm@...>, Ingo Molnar <mingo@...>
Cc: Randy Dunlap <randy.dunlap@...>, <yanzheng@...>, <linux-fsdevel@...>, <linux-kernel@...>, <linux-mm@...>, <ltp-list@...>
Subject: Re: [PATCH]fix VM_CAN_NONLINEAR check in sys_remap_file_pages
Date: Monday, October 8, 2007 - 3:45 am

Was probably found by review. Otherwise, you could probably reproduce

it by mmaping, say, drm device node, running remap_file_pages() on it

to create a nonlinear mapping, and then finding that you get the wrong


Here is Ingo's old test, since cleaned up and fixed a bit by me....

I'm sure he would distribute it GPL, but I've cc'ed him because I didn't

find an explicit statement about that.
[view original message]
From: WANG Cong <xiyou.wangcong@...>
To: Yan Zheng <yanzheng@...>
Cc: <linux-fsdevel@...>, <linux-kernel@...>, <akpm@...>
Subject: Re: [PATCH]fix VM_CAN_NONLINEAR check in sys_remap_file_pages
Date: Monday, October 8, 2007 - 7:52 am

Good catch!


! operator has higher priority than & operator.


-
Previous thread: [PATCH] virtualization of sysv msg queues is incomplete by Kirill Korotaev on Monday, October 8, 2007 - 7:05 am. (1 message)

Next thread: [PATCH 1/3] V4L: w9968cf, remove bad usage of ERESTARTSYS by Jiri Slaby on Monday, October 8, 2007 - 8:33 am. (16 messages)