On 10/26/20 9:48 AM, Andrey Zhadchenko wrote:
Use more generic igrab instead of atomic inc. Move cgroup_hash_del to eviction
stage to avoid deadlock.
Signed-off-by: Andrey Zhadchenko <andrey.zhadche...@virtuozzo.com>
---
kernel/cgroup.c | 25 ++++++++-----------------
1 file changed, 8 insertions(+), 17 deletions(-)
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 27d7a5e..3bcbae9 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -1522,21 +1522,10 @@ static struct inode *cgroup_find_inode(unsigned long
fh[2], char take_ref)
struct inode *ret = NULL;
spin_lock(&cgroup_inode_table_lock);
- item = cgroup_find_item_no_lock(fh);
- /*
- * If we need to increase refcount, we should be aware of possible
- * deadlock. Another thread may have started deleting this inode:
- * iput->iput_final->cgroup_delete_inode->cgroup_hash_del
- * If we just call igrab, it will try to take i_lock and this will
- * result in deadlock, because deleting thread has already taken it
- * and waits on cgroup_inode_table_lock to find inode in hashtable.
- *
- * If i_count is zero, someone is deleting it -> skip.
- */
- if (take_ref && item)
- if (!atomic_inc_not_zero(&item->inode->i_count))
- item = NULL;
+ item = cgroup_find_item_no_lock(fh);
+ if (item && take_ref && !igrab(item->inode))
+ item = NULL;
spin_unlock(&cgroup_inode_table_lock);
@@ -1634,15 +1623,17 @@ static const struct export_operations cgroup_export_ops = {
.fh_to_dentry = cgroup_fh_to_dentry,
};
-static int cgroup_delete_inode(struct inode *inode)
+static void cgroup_evict_inode(struct inode *inode)
{
cgroup_hash_del(inode);
- return generic_delete_inode(inode);
+ clear_inode(inode);
+ truncate_inode_pages_final(&inode->i_data);
Why clear_inode/truncate_inode_pages_final order is different from the
order in evict()? And probably also we need to call cgroup_hash_del
after clear_inode to be consistent with mqueue_evict_inode.
I don't like different order of calls in different places, though it is
probably ok now, this can hurt in future.
}
static const struct super_operations cgroup_ops = {
.statfs = simple_statfs,
- .drop_inode = cgroup_delete_inode,
+ .drop_inode = generic_delete_inode,
+ .evict_inode = cgroup_evict_inode,
.show_options = cgroup_show_options,
#ifdef CONFIG_VE
.show_path = cgroup_show_path,
--
Best regards, Tikhomirov Pavel
Software Developer, Virtuozzo.
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