linux-kernel - [PATCH 5/5] cachefiles: add missing lock protection when polling

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Date: Wed, 24 Apr 2024 11:34:09 +0800
From: libaokun@...weicloud.com
To: netfs@...ts.linux.dev
Cc: dhowells@...hat.com,
	jlayton@...nel.org,
	zhujia.zj@...edance.com,
	jefflexu@...ux.alibaba.com,
	linux-cachefs@...hat.com,
	linux-erofs@...ts.ozlabs.org,
	linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	libaokun@...weicloud.com,
	Joseph Qi <joseph.qi@...ux.alibaba.com>,
	Gao Xiang <hsiangkao@...ux.alibaba.com>,
	Baokun Li <libaokun1@...wei.com>
Subject: [PATCH 5/5] cachefiles: add missing lock protection when polling

From: Jingbo Xu <jefflexu@...ux.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 <jefflexu@...ux.alibaba.com>
Reviewed-by: Joseph Qi <joseph.qi@...ux.alibaba.com>
Reviewed-by: Gao Xiang <hsiangkao@...ux.alibaba.com>
Signed-off-by: Baokun Li <libaokun1@...wei.com>
---
 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))
-- 
2.39.2