Patch "cachefiles: make on-demand read killable" has been added to the 6.9-stable tree

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This is a note to let you know that I've just added the patch titled

    cachefiles: make on-demand read killable

to the 6.9-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     cachefiles-make-on-demand-read-killable.patch
and it can be found in the queue-6.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 40c6f12bec7fe2fb2622b780635c2b66f91f5bda
Author: Baokun Li <libaokun1@xxxxxxxxxx>
Date:   Wed May 22 19:43:08 2024 +0800

    cachefiles: make on-demand read killable
    
    [ Upstream commit bc9dde6155464e906e630a0a5c17a4cab241ffbb ]
    
    Replacing wait_for_completion() with wait_for_completion_killable() in
    cachefiles_ondemand_send_req() allows us to kill processes that might
    trigger a hunk_task if the daemon is abnormal.
    
    But now only CACHEFILES_OP_READ is killable, because OP_CLOSE and OP_OPEN
    is initiated from kworker context and the signal is prohibited in these
    kworker.
    
    Note that when the req in xas changes, i.e. xas_load(&xas) != req, it
    means that a process will complete the current request soon, so wait
    again for the request to be completed.
    
    In addition, add the cachefiles_ondemand_finish_req() helper function to
    simplify the code.
    
    Suggested-by: Hou Tao <houtao1@xxxxxxxxxx>
    Signed-off-by: Baokun Li <libaokun1@xxxxxxxxxx>
    Link: https://lore.kernel.org/r/20240522114308.2402121-13-libaokun@xxxxxxxxxxxxxxx
    Acked-by: Jeff Layton <jlayton@xxxxxxxxxx>
    Reviewed-by: Jia Zhu <zhujia.zj@xxxxxxxxxxxxx>
    Signed-off-by: Christian Brauner <brauner@xxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/fs/cachefiles/ondemand.c b/fs/cachefiles/ondemand.c
index a0e34581a1cd6..d0059d36cbd51 100644
--- a/fs/cachefiles/ondemand.c
+++ b/fs/cachefiles/ondemand.c
@@ -380,6 +380,20 @@ static struct cachefiles_req *cachefiles_ondemand_select_req(struct xa_state *xa
 	return NULL;
 }
 
+static inline bool cachefiles_ondemand_finish_req(struct cachefiles_req *req,
+						  struct xa_state *xas, int err)
+{
+	if (unlikely(!xas || !req))
+		return false;
+
+	if (xa_cmpxchg(xas->xa, xas->xa_index, req, NULL, 0) != req)
+		return false;
+
+	req->error = err;
+	complete(&req->done);
+	return true;
+}
+
 ssize_t cachefiles_ondemand_daemon_read(struct cachefiles_cache *cache,
 					char __user *_buffer, size_t buflen)
 {
@@ -443,16 +457,8 @@ ssize_t cachefiles_ondemand_daemon_read(struct cachefiles_cache *cache,
 out:
 	cachefiles_put_object(req->object, cachefiles_obj_put_read_req);
 	/* Remove error request and CLOSE request has no reply */
-	if (ret || msg->opcode == CACHEFILES_OP_CLOSE) {
-		xas_reset(&xas);
-		xas_lock(&xas);
-		if (xas_load(&xas) == req) {
-			req->error = ret;
-			complete(&req->done);
-			xas_store(&xas, NULL);
-		}
-		xas_unlock(&xas);
-	}
+	if (ret || msg->opcode == CACHEFILES_OP_CLOSE)
+		cachefiles_ondemand_finish_req(req, &xas, ret);
 	cachefiles_req_put(req);
 	return ret ? ret : n;
 }
@@ -557,8 +563,18 @@ static int cachefiles_ondemand_send_req(struct cachefiles_object *object,
 		goto out;
 
 	wake_up_all(&cache->daemon_pollwq);
-	wait_for_completion(&req->done);
-	ret = req->error;
+wait:
+	ret = wait_for_completion_killable(&req->done);
+	if (!ret) {
+		ret = req->error;
+	} else {
+		ret = -EINTR;
+		if (!cachefiles_ondemand_finish_req(req, &xas, ret)) {
+			/* Someone will complete it soon. */
+			cpu_relax();
+			goto wait;
+		}
+	}
 	cachefiles_req_put(req);
 	return ret;
 out:




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