linux-kernel - Re: [PATCH 3/5] dm: support retrieving struct dm_target from struct dm

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Date: Thu, 16 May 2024 12:39:08 -0400
From: Benjamin Marzinski <bmarzins@...hat.com>
To: YangYang <yang.yang@...o.com>
Cc: Alasdair Kergon <agk@...hat.com>, Mike Snitzer <snitzer@...nel.org>,
        Mikulas Patocka <mpatocka@...hat.com>, dm-devel@...ts.linux.dev,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/5] dm: support retrieving struct dm_target from struct
 dm_dev

On Thu, May 16, 2024 at 10:12:25AM +0800, YangYang wrote:
> On 2024/5/16 0:00, Benjamin Marzinski wrote:
> > On Wed, May 15, 2024 at 11:42:04AM -0400, Benjamin Marzinski wrote:
> > > When a target calls dm_get_device(), if it adds a new table device to
> > > t->devices, then it's the first target in this table to use that device.
> > > If flush_pass_around is set for this target, then it also sets
> > > sends_pass_around_flush. In __send_empty_flush() if the table has
> > > flush_pass_around set, when you iterate through the devices, you only
> > 
> > Err, "When you iterate through the *targets*, you only ..." In this
> > method you don't iterate through the list of devices (which is supposed
> > to be protected by t->devices_lock).
> 
> I'm not very familiar with this area, I thought that the device list
> of an active table cannot be modified, so it doesn't need to be
> protected by t->devices_lock.

Actually, looking at this some more you're basically correct. The only
place where dm can modify the devices list of active table is in
multipath_message(), and that's bug. So you should be safe not locking
here.

I'll post a patch to fix the multipath target.

-Ben
 
> > 
> > > call __send_empty_flush_bios() for the ones with sends_pass_around_flush
> > > set.
> > > 
> > > Or am I overlooking something?
> > > 
> > > -Ben
> >