Messages in this thread | | | Date | Mon, 4 Jul 2022 13:01:14 +0200 | From | Greg KH <> | Subject | Re: [PATCH] char: misc: make misc_open() and misc_register() killable |
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On Mon, Jul 04, 2022 at 07:25:44PM +0900, Tetsuo Handa wrote: > On 2022/07/04 16:29, Greg KH wrote: > > On Mon, Jul 04, 2022 at 03:44:07PM +0900, Tetsuo Handa wrote: > >> syzbot is reporting hung task at misc_open() [1], for snapshot_open() from > >> misc_open() might sleep for long with misc_mtx held whereas userspace can > >> flood with concurrent misc_open() requests. Mitigate this problem by making > >> misc_open() and misc_register() killable. > > > > I do not understand, why not just fix snapshot_open()? Why add this > > complexity to the misc core for a foolish individual misc device? Why > > not add the fix there where it is spinning instead? > > Quoting an example from [1]. Multiple processes are calling misc_open() and > all but one processes are blocked at mutex_lock(&misc_mtx). The one which is > not blocked at mutex_lock(&misc_mtx) is also holding system_transition_mutex.
And that is because of that one misc device, right? Why not fix that instead of papering over the issue in the misc core?
thanks,
greg k-h
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