[PATCH v3 9/9] cachefiles: add missing lock protection when polling

[libaokun]

From: Jingbo Xu <jeffl...@linux.alibaba.com>

Add missing lock protection in poll routine when iterating xarray,
otherwise:

Even with RCU read lock held, only the slot of the radix tree is
ensured to be pinned there, while the data structure (e.g. struct
cachefiles_req) stored in the slot has no such guarantee.  The poll
routine will iterate the radix tree and dereference cachefiles_req
accordingly.  Thus RCU read lock is not adequate in this case and
spinlock is needed here.

Fixes: b817e22b2e91 ("cachefiles: narrow the scope of triggering EPOLLIN events 
in ondemand mode")
Signed-off-by: Jingbo Xu <jeffl...@linux.alibaba.com>
Signed-off-by: Baokun Li <libaok...@huawei.com>
Reviewed-by: Jia Zhu <zhujia...@bytedance.com>
Reviewed-by: Gao Xiang <hsiang...@linux.alibaba.com>
Acked-by: Jeff Layton <jlay...@kernel.org>
---
 fs/cachefiles/daemon.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/cachefiles/daemon.c b/fs/cachefiles/daemon.c
index 06cdf1a8a16f..89b11336a836 100644
--- a/fs/cachefiles/daemon.c
+++ b/fs/cachefiles/daemon.c
@@ -366,14 +366,14 @@ static __poll_t cachefiles_daemon_poll(struct file *file,
 
        if (cachefiles_in_ondemand_mode(cache)) {
                if (!xa_empty(&cache->reqs)) {
-                       rcu_read_lock();
+                       xas_lock(&xas);
                        xas_for_each_marked(&xas, req, ULONG_MAX, 
CACHEFILES_REQ_NEW) {
                                if 
(!cachefiles_ondemand_is_reopening_read(req)) {
                                        mask |= EPOLLIN;
                                        break;
                                }
                        }
-                       rcu_read_unlock();
+                       xas_unlock(&xas);
                }
        } else {
                if (test_bit(CACHEFILES_STATE_CHANGED, &cache->flags))
-- 
2.39.2