While running a bind/unbind stress test with the dwc3 usb driver on rk3399, the following crash was observed. Unable to handle kernel NULL pointer dereference at virtual address 00000218 pgd = ffffffc00165f000 [00000218] *pgd=000000000174f003, *pud=000000000174f003, *pmd=0000000001750003, *pte=00e8000001751713 Internal error: Oops: 96000005 [#1] PREEMPT SMP Modules linked in: uinput uvcvideo videobuf2_vmalloc cmac ipt_MASQUERADE nf_nat_masquerade_ipv4 iptable_nat nf_nat_ipv4 nf_nat rfcomm xt_mark fuse bridge stp llc zram btusb btrtl btbcm btintel bluetooth ip6table_filter mwifiex_pcie mwifiex cfg80211 cdc_ether usbnet r8152 mii joydev snd_seq_midi snd_seq_midi_event snd_rawmidi snd_seq snd_seq_device ppp_async ppp_generic slhc tun CPU: 1 PID: 29814 Comm: kworker/1:1 Not tainted 4.4.52 #507 Hardware name: Google Kevin (DT) Workqueue: pm pm_runtime_work task: ffffffc0ac540000 ti: ffffffc0af4d4000 task.ti: ffffffc0af4d4000 PC is at autosuspend_check+0x74/0x174 LR is at autosuspend_check+0x70/0x174 ... Call trace: [<ffffffc00080dcc0>] autosuspend_check+0x74/0x174 [<ffffffc000810500>] usb_runtime_idle+0x20/0x40 [<ffffffc000785ae0>] __rpm_callback+0x48/0x7c [<ffffffc000786af0>] rpm_idle+0x1e8/0x498 [<ffffffc000787cdc>] pm_runtime_work+0x88/0xcc [<ffffffc000249bb8>] process_one_work+0x390/0x6b8 [<ffffffc00024abcc>] worker_thread+0x480/0x610 [<ffffffc000251a80>] kthread+0x164/0x178 [<ffffffc0002045d0>] ret_from_fork+0x10/0x40 Source: (gdb) l *0xffffffc00080dcc0 0xffffffc00080dcc0 is in autosuspend_check (drivers/usb/core/driver.c:1778). 1773 /* We don't need to check interfaces that are 1774 * disabled for runtime PM. Either they are unbound 1775 * or else their drivers don't support autosuspend 1776 * and so they are permanently active. 1777 */ 1778 if (intf->dev.power.disable_depth) 1779 continue; 1780 if (atomic_read(&intf->dev.power.usage_count) > 0) 1781 return -EBUSY; 1782 w |= intf->needs_remote_wakeup; Code analysis shows that intf is set to NULL in usb_disable_device() prior to setting actconfig to NULL. At the same time, usb_runtime_idle() does not lock the usb device, and neither does any of the functions in the traceback. This means that there is no protection against a race condition where usb_disable_device() is removing dev->actconfig->interface[] pointers while those are being accessed from autosuspend_check() and possibly by other callers. Explicitly disable autosuspend in usb_disconnect() before calling usb_disable_device(). This doesn't fix the race for good, but it ensures that the pm runtime worker doesn't call usb_runtime_idle() on the interface that is being removed, and thus avoids the race in the affected code path. Signed-off-by: Guenter Roeck <linux@xxxxxxxxxxxx> --- This is another interesting situation. As mentioned above, the patch doesn't really fix the race problem. On the other side, fixing it for good would (probably) be much more complex. I still see the race after applying this patch, but it happens maybe once a day vs. several times per hour. Marked as RFC in the hope that someone has an idea for a better fix. I tried clearing udev->actconfig prior to removing the interfaces in usb_disable_device(), but that alone didn't help; it does not resolve the race condition either, and still results in the crash. The only clean solution I can think of would be to protect accesses to dev->actconfig with a spinlock or mutex, and to make sure that the lock is held during read accesses and that dev->actconfig is cleared before releasing the lock on write accesses. I'll be happy to do that if it is the way to go, but I would like some feedback before I give it a try. drivers/usb/core/hub.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c index 5286bf67869a..5a420657f9f7 100644 --- a/drivers/usb/core/hub.c +++ b/drivers/usb/core/hub.c @@ -2093,6 +2093,15 @@ void usb_disconnect(struct usb_device **pdev) * so that the hardware is now fully quiesced. */ dev_dbg(&udev->dev, "unregistering device\n"); + + /* + * Disable autosuspend before disabling the device, and make sure + * that autosuspend doesn't touch it while it is in the process + * of being deleted. + */ + usb_disable_autosuspend(udev); + pm_runtime_barrier(&udev->dev); + usb_disable_device(udev, 0); usb_hcd_synchronize_unlinks(udev); -- 2.7.4 -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
