Messages in this thread | | | Date | Sun, 19 May 2013 23:35:51 +0300 | From | "Michael S. Tsirkin" <> | Subject | Re: [PATCH v2 10/10] kernel: might_fault does not imply might_sleep |
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On Sun, May 19, 2013 at 04:23:22PM -0400, Steven Rostedt wrote: > On Sun, 2013-05-19 at 19:40 +0300, Michael S. Tsirkin wrote: > > > OK I get it. So let me correct myself. The simple code > > that does something like this under a spinlock: > > > preempt_disable > > > pagefault_disable > > > error = copy_to_user > > > pagefault_enable > > > preempt_enable > > > > > is not doing anything wrong and should not get a warning, > > as long as error is handled correctly later. > > Right? > > I came in mid thread and I don't know the context.
The context is that I want to change might_fault from might_sleep to might_sleep_if(!in_atomic()) so that above does not trigger warnings even with CONFIG_DEBUG_ATOMIC_SLEEP enabled.
> Anyway, the above > looks to me as you just don't want to sleep.
Exactly. upstream we can just do pagefault_disable but to make this code -rt ready it's best to do preempt_disable as well.
> If you try to copy data to > user space that happens not to be currently mapped for any reason, you > will get an error. Even if the address space is completely valid. Is > that what you want? > > -- Steve >
Yes, this is by design. We detect that and bounce the work to a thread outside any locks.
Thanks,
-- MST
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