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| author | Muchun Song <songmuchun@bytedance.com> | 2021-04-02 17:11:45 +0800 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2021-07-20 16:15:52 +0200 |
| commit | fdf3ef3f66cb88f30fbf9396f876937b29506d9b (patch) | |
| tree | 3938eb70f88244e7b0b33983d2adf0c1d8f579f5 | |
| parent | 4a808634e5a6eb74eb7423cb999c1892a5c7b547 (diff) | |
| download | linux-stable-fdf3ef3f66cb88f30fbf9396f876937b29506d9b.tar.gz linux-stable-fdf3ef3f66cb88f30fbf9396f876937b29506d9b.tar.bz2 linux-stable-fdf3ef3f66cb88f30fbf9396f876937b29506d9b.zip | |
writeback: fix obtain a reference to a freeing memcg css
[ Upstream commit 8b0ed8443ae6458786580d36b7d5f8125535c5d4 ]
The caller of wb_get_create() should pin the memcg, because
wb_get_create() relies on this guarantee. The rcu read lock
only can guarantee that the memcg css returned by css_from_id()
cannot be released, but the reference of the memcg can be zero.
rcu_read_lock()
memcg_css = css_from_id()
wb_get_create(memcg_css)
cgwb_create(memcg_css)
// css_get can change the ref counter from 0 back to 1
css_get(memcg_css)
rcu_read_unlock()
Fix it by holding a reference to the css before calling
wb_get_create(). This is not a problem I encountered in the
real world. Just the result of a code review.
Fixes: 682aa8e1a6a1 ("writeback: implement unlocked_inode_to_wb transaction and use it for stat updates")
Link: https://lore.kernel.org/r/20210402091145.80635-1-songmuchun@bytedance.com
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Sasha Levin <sashal@kernel.org>
| -rw-r--r-- | fs/fs-writeback.c | 9 |
1 files changed, 7 insertions, 2 deletions
diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c index fc9167e65287..869a34a48958 100644 --- a/fs/fs-writeback.c +++ b/fs/fs-writeback.c @@ -512,9 +512,14 @@ static void inode_switch_wbs(struct inode *inode, int new_wb_id) /* find and pin the new wb */ rcu_read_lock(); memcg_css = css_from_id(new_wb_id, &memory_cgrp_subsys); - if (memcg_css) - isw->new_wb = wb_get_create(bdi, memcg_css, GFP_ATOMIC); + if (memcg_css && !css_tryget(memcg_css)) + memcg_css = NULL; rcu_read_unlock(); + if (!memcg_css) + goto out_free; + + isw->new_wb = wb_get_create(bdi, memcg_css, GFP_ATOMIC); + css_put(memcg_css); if (!isw->new_wb) goto out_free; |