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author | Muchun Song <songmuchun@bytedance.com> | 2021-04-02 12:11:45 +0300 |
---|---|---|
committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2021-07-14 17:53:35 +0300 |
commit | 5c93fc46682c18c0cac60e09d1e6d375a30c7a85 (patch) | |
tree | d8f8d8b19f9cdaad94b7b67dfdd4c72d46de6221 /fs | |
parent | 71721ddf4aee271af6e1d7682da6a90a76ccd5a5 (diff) | |
download | linux-5c93fc46682c18c0cac60e09d1e6d375a30c7a85.tar.xz |
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>
Diffstat (limited to 'fs')
-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 3a0d7b8af141..22e9c88f3960 100644 --- a/fs/fs-writeback.c +++ b/fs/fs-writeback.c @@ -510,9 +510,14 @@ 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; |