Re: [PATCH] nfc/nci: fix task hung in nfc_targets_found

On 2024/01/15 18:36, Krzysztof Kozlowski wrote:

quoted

diff --git a/net/nfc/nci/core.c b/net/nfc/nci/core.c
index 6c9592d05120..9a277228a875 100644
--- a/net/nfc/nci/core.c
+++ b/net/nfc/nci/core.c

@@ -145,6 +145,8 @@ inline int nci_request(struct nci_dev *ndev,
 {
 	int rc;
 
+	if (test_bit(NCI_UNREG, &ndev->flags))
+		return -ENODEV;

nci_close_device() clears the NCI_UP, which is tested here, just after
acquiring mutex. And there is explicit comment about it just below your
code. Why it is not relevant?

Because the deadlock happens at mutex_lock(&ndev->req_lock), which is
before test_bit(NCI_UP, &ndev->flags) is called. Please see
https://lkml.kernel.org/r/d314e471-0251-461e-988d-70add0c6ebf6@I-love.SAKURA.ne.jp .

Your code looks really unnecessary, at least with that code flow from
commit msg. Especially considering you do it outside of mutex, so how
does it solve anything?

Best regards,
Krzysztof