Re: [PATCH 5/5] cachefiles: add missing lock protection when polling

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在 2024/4/24 11:34, libaokun@xxxxxxxxxxxxxxx 写道:
From: Jingbo Xu <jefflexu@xxxxxxxxxxxxxxxxx>

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 <jefflexu@xxxxxxxxxxxxxxxxx>
Reviewed-by: Joseph Qi <joseph.qi@xxxxxxxxxxxxxxxxx>
Reviewed-by: Gao Xiang <hsiangkao@xxxxxxxxxxxxxxxxx>
Signed-off-by: Baokun Li <libaokun1@xxxxxxxxxx>

Thanks for catching this.

Reviewed-by: Jia Zhu <zhujia.zj@xxxxxxxxxxxxx>

---
  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 6465e2574230..73ed2323282a 100644
--- a/fs/cachefiles/daemon.c
+++ b/fs/cachefiles/daemon.c
@@ -365,14 +365,14 @@ 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))




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