linux-kernel - Re: [syzbot] BUG: sleeping function called from invalid context in hci_cmd_sync

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Date:   Thu, 09 Dec 2021 13:46:47 +0100
From:   Benjamin Berg <bberg@...hat.com>
To:     Oliver Neukum <oneukum@...e.com>,
        syzbot <syzbot+485cc00ea7cf41dfdbf1@...kaller.appspotmail.com>,
        Thinh.Nguyen@...opsys.com, changbin.du@...el.com,
        christian.brauner@...ntu.com, davem@...emloft.net,
        edumazet@...gle.com, gregkh@...uxfoundation.org,
        johan.hedberg@...il.com, kuba@...nel.org,
        linux-bluetooth@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-usb@...r.kernel.org, luiz.dentz@...il.com,
        luiz.von.dentz@...el.com, marcel@...tmann.org,
        mathias.nyman@...ux.intel.com, netdev@...r.kernel.org,
        stern@...land.harvard.edu, syzkaller-bugs@...glegroups.com,
        yajun.deng@...ux.dev
Subject: Re: [syzbot] BUG: sleeping function called from invalid context in
 hci_cmd_sync_cancel

Hi,

On Thu, 2021-12-09 at 11:06 +0100, Oliver Neukum wrote:
> As __cancel_work_timer can be called from hci_cmd_sync_cancel() this is
> just not
> an approach you can take. It looks like asynchronously canceling the
> scheduled work
> would result in a race, so I would for now just revert.

Right, so this needs to be pushed into a workqueue instead, I suppose.

> What issue exactly is this trying to fix or improve?

The problem is aborting long-running synchronous operations. i.e.
without this patchset, USB enumeration will hang for 10s if a USB
bluetooth device disappears during firmware loading. This is because
even though the USB device is gone and all URB submissions fail, the
operation will only be aborted after the internal timeout happens.

The device in turn disappears because an rfkill switch is blocked and
the platform removes it from the bus. Overall, this can lead to
graphical login to hang as fprintd cannot initialise as it hangs in USB
enumeration.

Benjamin

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