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author | Dennis Zhou (Facebook) <dennisszhou@gmail.com> | 2018-09-11 14:41:26 -0400 |
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committer | Jens Axboe <axboe@kernel.dk> | 2018-09-21 20:29:02 -0600 |
commit | 27e6fa996c534c32702aa4d32db0ffa383acd050 (patch) | |
tree | fbeed4501b887851cc4b48af3ddb9d24d8e2dd9f /block/blk-cgroup.c | |
parent | 9ff01255a01c3d6ffc8670b358b3ac567d5646fc (diff) |
blkcg: fix ref count issue with bio_blkcg using task_css
The accessor function bio_blkcg either returns the blkcg associated with
the bio or finds one in the current context. This can cause an issue
when trying to associate a bio with a blkcg. Particularly, it's the
third case that is problematic:
return css_to_blkcg(task_css(current, io_cgrp_id));
As the above may race against task migration and the cgroup exiting, it
is not always ok to take a reference on the blkcg returned from
bio_blkcg.
This patch adds association ahead of calling bio_blkcg rather than
after. This makes association a required and explicit step along the
code paths for calling bio_blkcg. blk_get_rl is modified as well to get
a reference to the blkcg it may use and blk_put_rl will always put the
reference back. Association is also moved above the bio_blkcg call to
ensure it will not return NULL in blk-iolatency.
BFQ and CFQ utilize this flaw, but due to the complexity, I do not want
to address this in this series. I've created a private version of the
function with notes not to use it describing the flaw. Hopefully soon,
that code can be cleaned up.
Signed-off-by: Dennis Zhou <dennisszhou@gmail.com>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'block/blk-cgroup.c')
0 files changed, 0 insertions, 0 deletions