linux-kernel - Re: [PATCH] Fix queueing work if !bdi_cap_writeback

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <871ui6e4tl.fsf@devron.myhome.or.jp>
Date:	Thu, 13 Sep 2012 16:53:58 +0900
From:	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
To:	Fengguang Wu <fengguang.wu@...el.com>
Cc:	viro@...iv.linux.org.uk, jack@...e.cz, hch@....de,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Fix queueing work if !bdi_cap_writeback_dirty()

Fengguang Wu <fengguang.wu@...el.com> writes:

> On Wed, Sep 12, 2012 at 03:28:42AM +0900, OGAWA Hirofumi wrote:
>> 
>> If bdi has BDI_CAP_NO_WRITEBACK, bdi_forker_thread() doesn't start
>> writeback thread. This means there is no consumer of work item made
>> by bdi_queue_work().
>> 
>> This adds to checking of !bdi_cap_writeback_dirty(sb->s_bdi) before
>> calling bdi_queue_work(), otherwise queued work never be consumed.
>> 
>> Signed-off-by: OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
>> ---
>> 
>>  fs/fs-writeback.c |    7 +++++--
>>  1 file changed, 5 insertions(+), 2 deletions(-)
>> 
>> diff -puN fs/fs-writeback.c~noop_backing_dev_info-check-fix fs/fs-writeback.c
>> --- linux/fs/fs-writeback.c~noop_backing_dev_info-check-fix	2012-09-11 06:12:30.000000000 +0900
>> +++ linux-hirofumi/fs/fs-writeback.c	2012-09-11 06:12:30.000000000 +0900
>> @@ -120,6 +120,9 @@ __bdi_start_writeback(struct backing_dev
>>  {
>>  	struct wb_writeback_work *work;
>>  
>> +	if (!bdi_cap_writeback_dirty(bdi))
>> +		return;
>
> Will someone in the current kernel actually call
> __bdi_start_writeback() on a BDI_CAP_NO_WRITEBACK bdi?
>
> If the answer is no, VM_BUG_ON(!bdi_cap_writeback_dirty(bdi)) looks better.

I guess nobody call it in current kernel though. Hmm.., but we also have
check in __mark_inode_dirty(), nobody should be using it, right?

If we defined it as the bug, I can't see what BDI_CAP_NO_WRITEBACK wants
to do actually.  We are not going to allow to disable the writeback task?

I was going to use this to disable writeback task on my developing FS...

Thanks.
-- 
OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/