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fs: rotate inodes whose page cache could not be dropped

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When inode_lru_isolate() drops the page cache of an unused inode, it
has to unlock the list, so it returns LRU_RETRY and the walk restarts
at the head of the list, where the inode still is. If
invalidate_mapping_pages() could not empty the mapping, the restarted
walk strips the same inode again, and so on until nr_to_walk runs out.
Every walk of that list then ends on this inode, and nothing behind it
is reclaimed for as long as its cache stays.

Before commit 2a0629834c ("vfs: Don't evict inode under the inode lru
traversing context") the walker pinned the inode with a reference, and
dropping it in iput_final() set I_REFERENCED, so the restarted walk
rotated the inode to the tail. Set I_REFERENCED again when the mapping
is still populated after the invalidation, in the same i_lock section
that clears I_LRU_ISOLATING. inode_unpin_lru_isolating() now expects
i_lock to be held, like inode_pin_lru_isolating().

On CONFIG_HIGHMEM kernels this can happen to any unused inode: a folio
is left behind if it is locked, under writeback, spliced into a pipe,
or still in another CPU's LRU-add batch after being read. Without
HIGHMEM it happens to DAX inodes whose only entry is at index 0, which
mapping_shrinkable() lets onto the LRU and invalidate_mapping_pages()
never removes.

Fixes: 2a0629834c ("vfs: Don't evict inode under the inode lru traversing context")
Cc: stable@vger.kernel.org
Signed-off-by: Nikolaos Karaolidis <nick@karaolidis.com>
Link: https://patch.msgid.link/20261016102515.111285-1-nick@karaolidis.com
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Zhihao Cheng <chengzhihao1@huawei.com>
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
This commit is contained in:
Nikolaos Karaolidis 2026-10-16 10:25:15 +00:00 committed by Christian Brauner
parent 46e66d41fa
commit 8ee09f5977
No known key found for this signature in database
GPG Key ID: 91C61BC06578DCA2
1 changed files with 7 additions and 2 deletions
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9
fs/inode.c
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@ -593,12 +593,11 @@ static void inode_pin_lru_isolating(struct inode *inode)
static void inode_unpin_lru_isolating(struct inode *inode)
{
spin_lock(&inode->i_lock);
lockdep_assert_held(&inode->i_lock);
WARN_ON(!(inode_state_read(inode) & I_LRU_ISOLATING));
inode_state_clear(inode, I_LRU_ISOLATING);
/* Called with inode->i_lock which ensures memory ordering. */
inode_wake_up_bit(inode, __I_LRU_ISOLATING);
spin_unlock(&inode->i_lock);
}
static void inode_wait_for_lru_isolating(struct inode *inode)
@ -981,7 +980,13 @@ static enum lru_status inode_lru_isolate(struct list_head *item,
else
__count_vm_events(PGINODESTEAL, reap);
mm_account_reclaimed_pages(reap);
spin_lock(&inode->i_lock);
/* The walk restarts here: don't retry leftovers right away */
if (!mapping_empty(&inode->i_data))
inode_state_set(inode, I_REFERENCED);
inode_unpin_lru_isolating(inode);
spin_unlock(&inode->i_lock);
return LRU_RETRY;
}