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| author | Muchun Song <songmuchun@bytedance.com> | 2021-04-02 17:11:45 +0800 |
|---|---|---|
| committer | Jan Kara <jack@suse.cz> | 2021-06-28 18:35:02 +0200 |
| commit | 8b0ed8443ae6458786580d36b7d5f8125535c5d4 (patch) | |
| tree | 4cb9fc32fd24cb332daeb2cbd6d0715d43a06828 /fs/fs-writeback.c | |
| parent | ce1b06c5f5e7fd2af8bc89323d9eb3102d8e3fe2 (diff) | |
| download | linux-8b0ed8443ae6458786580d36b7d5f8125535c5d4.tar.gz linux-8b0ed8443ae6458786580d36b7d5f8125535c5d4.tar.bz2 linux-8b0ed8443ae6458786580d36b7d5f8125535c5d4.zip | |
writeback: fix obtain a reference to a freeing memcg css
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>
Diffstat (limited to 'fs/fs-writeback.c')
| -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 e91980f49388..d52c291d7bcd 100644 --- a/fs/fs-writeback.c +++ b/fs/fs-writeback.c @@ -508,9 +508,14 @@ 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; |