Messages in this thread | | | Date | Tue, 27 Sep 2022 13:20:38 +0200 | From | "Jason A. Donenfeld" <> | Subject | Re: [PATCH v4 2/2] lib/vsprintf: Initialize vsprintf's pointer hash once the random core is ready. |
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You added my Acked-by already (which is fine), but I thought I should still add some final notes to that ack, for posterity:
On Tue, Sep 27, 2022 at 12:49:12PM +0200, Sebastian Andrzej Siewior wrote: > The printk code invokes vnsprintf in order to compute the complete > string before adding it into its buffer. This happens in an IRQ-off > region which leads to a warning on PREEMPT_RT in the random code if the > format strings contains a %p for pointer printing. This happens because > the random core acquires locks which become sleeping locks on PREEMPT_RT > which must not be acquired with disabled interrupts and or preemption > disabled. > By default the pointers are hashed which requires a random value on the > first invocation (either by printk or another user which comes first. > > One could argue that there is no need for printk to disable interrupts > during the vsprintf() invocation which would fix the just mentioned > problem. However printk itself can be invoked in a context with > disabled interrupts which would lead to the very same problem. > > Move the initialization of ptr_key into a worker and schedule it from > subsys_initcall(). This happens early but after the workqueue subsystem > is ready. Use get_random_bytes() to retrieve the random value if the RNG > core is ready, otherwise schedule a worker in two seconds and try again. > > Reported-by: Mike Galbraith <efault@gmx.de> > Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> > Acked-by: Jason A. Donenfeld <Jason@zx2c4.com>
I really do hate the idea of polling every 2 seconds. But as we discussed, this seems like the least bad solution, at least for now. If we discover another bug in the tree that needs a gross solution like that, then at that point, I'll move ahead with adding a notifier_block to random.c, to avoid polling. But so long as this is a one-off (as we understand it to be at the moment), this seems okay.
Acked-by: Jason A. Donenfeld <Jason@zx2c4.com>
Jason
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