Hi,

On 2020/2/19 20:55, Jan Kara wrote:

Hi!

On Sat 15-02-20 21:54:08, Yufen Yu wrote:

I've now noticed there's commit 68f23b8906 "memcg: fix a crash in wb_workfn
when a device disappears" from end of January which tries to address the
issue you're looking into. Now AFAIU the code is till somewhat racy after
that commit so I wanted to mention this mostly so that you fixup also the
new bdi_dev_name() while you're fixing blkg_dev_name().

Also I was wondering about one thing: If we really care about bdi->dev only
for the name, won't we be much better off with just copying the name to
bdi->name on registration? Sure it would consume a bit of memory for the
name copy but I don't think we really care and things would be IMO *much*
simpler that way... Yufen, Tejun, what do you think?

I think copying the name to bdi->name is also need protected by lock.
Otherwise, the reader of bdi->name may read incorrect value when
re-registion have not copy the name completely. Right? So, I also think
using RCU to protect object lifetimes may be a better way.

Thanks,
Yufen