Messages in this thread | | | Date | Mon, 1 Aug 2022 14:36:48 +0200 | From | "Jason A. Donenfeld" <> | Subject | Re: [PATCH 2/2 v3] lib/vsprintf: Initialize vsprintf's pointer hash once the random core is ready. |
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On Mon, Aug 01, 2022 at 11:34:26AM +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> > --- > v2…v3: > - schedule a worker every two seconds if the RNG core is not ready. > > lib/vsprintf.c | 46 +++++++++++++++++++++++++++------------------- > 1 file changed, 27 insertions(+), 19 deletions(-) > > --- a/lib/vsprintf.c > +++ b/lib/vsprintf.c > @@ -751,31 +751,39 @@ static int __init debug_boot_weak_hash_e > early_param("debug_boot_weak_hash", debug_boot_weak_hash_enable); > > static bool filled_random_ptr_key; > +static siphash_key_t ptr_key __read_mostly; > +static void fill_ptr_key_workfn(struct work_struct *work); > +static DECLARE_DELAYED_WORK(fill_ptr_key_work, fill_ptr_key_workfn); > + > +static void fill_ptr_key_workfn(struct work_struct *work) > +{ > + if (!rng_is_initialized()) { > + queue_delayed_work(system_unbound_wq, &fill_ptr_key_work, HZ * 2); > + return; > + }
This seems kind of crazy and over-complex. You only need this on RT, right? Because of the raw lock issue? So just schedule it for the right time on RT and not elsewhere.
I'll send a more basic patch.
Jason
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