Messages in this thread | | | Date | Fri, 18 Sep 2020 10:22:32 +0200 | From | peterz@infradea ... | Subject | Re: [patch 09/10] sched/core: Add migrate_disable/enable() |
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On Thu, Sep 17, 2020 at 06:30:01PM +0200, Sebastian Siewior wrote: > On 2020-09-17 17:54:10 [+0200], peterz@infradead.org wrote: > > I'm not sure what the problem with FPU was, I was throwing alternatives > > at tglx to see what would stick, in part to (re)discover the design > > constraints of this thing. > > was this recent or distant in the time line?
The past few weeks :-) Thomas and me have been bickering about this stuff on IRC on and off.
> > One reason for not allowing migrate_disable() to sleep was: FPU code. > > > > Could it be it does something like: > > > > preempt_disable(); > > spin_lock(); > > > > spin_unlock(); > > preempt_enable(); > > > > Where we'll never get preempted while migrate_disable()'d and thus never > > trigger any of the sleep paths? > > I try to get rid of something like that. This doesn't work either way > because the spin_lock() may block which it can't with disabled > preemption.
Yeah, that obviously should have been migrate_disable/enable instead of spin_lock/unlock :/
> Ah. We used to have migrate_disable() in pagefault_disable(). The x86 > FPU code does > preempt_disable(); > … > pagefault_disable(); > > but that migrate_disable() was moved from pagefault_disable() to > kmap_atomic(). We shouldn't have > preempt_disable(); || local_irq_disable(); > kmap_atomic(); > > on RT. I've been running around removing those. See > a10dcebacdb0c ("fs/ntfs/aops.c: don't disable interrupts during kmap_atomic()") > ce1e518190ea7 ("ide: don't disable interrupts during kmap_atomic()") > f3a1075e5fc34 ("block: don't disable interrupts during kmap_atomic()")
Hmm, okay.
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