| Message ID | tencent_E44436084AA874977705670A3CDD37BE9609@qq.com (mailing list archive) |
|---|---|
| State | Not Applicable |
| Delegated to: | Netdev Maintainers |
| Headers | show |
| Series | nfc/nci: fix task hung in nfc_targets_found | expand |
On 14/01/2024 09:20, Edward Adam Davis wrote: > nci_start_poll() holds the dev->mutex required by the kworker of nci_close_device(), > and the related tasks are as follows: > |cpu0 |cpu1 |cpu2 | > |nci_close_device() | | | > |mutex_lock(&ndev->req_lock); | | | > |... |nfc_genl_start_poll() | | > |flush_workqueue(ndev->rx_wq) |mutex_lock(&dev->genl_data.genl_data_mutex); | | > | |nfc_start_poll() | | > | |device_lock(&dev->dev); |process_one_work() | > | |nci_start_poll() |nfc_targets_found() | > | |nci_request() |device_lock(&dev->dev); | > | |mutex_lock(&ndev->req_lock); | | > > Therefore, before applying for req_lock in nci_request(), it should be determined > whether the execution of nci_close_device() has already begun. > > Reported-and-tested-by: syzbot+2b131f51bb4af224ab40@syzkaller.appspotmail.com > Signed-off-by: Edward Adam Davis <eadavis@qq.com> > --- > net/nfc/nci/core.c | 2 ++ > 1 file changed, 2 insertions(+) > > 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? 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
On 2024/01/15 18:36, Krzysztof Kozlowski wrote: >> 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 >
On 15/01/2024 12:08, Tetsuo Handa wrote: > On 2024/01/15 18:36, Krzysztof Kozlowski wrote: >>> 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 . I see, yet still this code looks like moving or copying existing test_bit(NCI_UP) outside of mutex, which is usually not the correct solution for deadlocks. First of all, flags are supposed to be manipulated under lock, so the code here can be quite re-ordered. What stops the CPU to test negative in above (so: !NCI_UNREG) and then execute nci_close_device before waiting on mutex here? Nothing. The problem seems to be locking and solution is not to add one if() outside of locking. Best regards, Krzysztof
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; /* Serialize all requests */ mutex_lock(&ndev->req_lock); /* check the state after obtaing the lock against any races
nci_start_poll() holds the dev->mutex required by the kworker of nci_close_device(), and the related tasks are as follows: |cpu0 |cpu1 |cpu2 | |nci_close_device() | | | |mutex_lock(&ndev->req_lock); | | | |... |nfc_genl_start_poll() | | |flush_workqueue(ndev->rx_wq) |mutex_lock(&dev->genl_data.genl_data_mutex); | | | |nfc_start_poll() | | | |device_lock(&dev->dev); |process_one_work() | | |nci_start_poll() |nfc_targets_found() | | |nci_request() |device_lock(&dev->dev); | | |mutex_lock(&ndev->req_lock); | | Therefore, before applying for req_lock in nci_request(), it should be determined whether the execution of nci_close_device() has already begun. Reported-and-tested-by: syzbot+2b131f51bb4af224ab40@syzkaller.appspotmail.com Signed-off-by: Edward Adam Davis <eadavis@qq.com> --- net/nfc/nci/core.c | 2 ++ 1 file changed, 2 insertions(+)