On Fri, Aug 13, 2021 at 6:34 PM Xiao Ni [off-list ref] wrote:
Hi Song
It can improve the performance. It needs to add rcu lock when calling
rcu_dereference.
Now it has a bug. It doesn't use rcu lock to protect. In the second
loop, it doesn't need
to use rcu_dereference when getting rdev. So to resolve this bug, we can remove
rcu_dereference directly.
In the second loop, we only use rdev and rrdev when bio and repl_bio
exists. So we shouldn't trigger the "bug" in any cases, right?
Please:
1) If you do think this is a bug, add a fix tag, so we can back port to stable.
(while I still think it is not a real bug).
2) move struct md_rdev *rdev = rcu_dereference(conf->mirrors[disk].rdev); to
under "if (r10_bio->devs[disk].bio)"; and the rrdev ... to "if
(repl_bio)". And add
a comment there so it is more clear in the code.
Thanks,
Song