Re: [PATCH v2] mm/page_isolation: fix a deadlock with printk()

Sergey Senozhatsky
2019-10-10T05:14:22Z

On (10/09/19 16:26), Michal Hocko wrote:
> On Wed 09-10-19 15:56:32, Peter Oberparleiter wrote:
> [...]
> > A generic solution would be preferable from my point of view though,
> > because otherwise each console driver owner would need to ensure that any
> > lock taken in their console.write implementation is never held while
> > memory is allocated/released.
>
> Considering that console.write is called from essentially arbitrary code
> path IIUC then all the locks used in this path should be pretty much
> tail locks or console internal ones without external dependencies.

That's a good expectation, but I guess it's not always the case.

One example might be NET console - net subsystem locks, net device
drivers locks, maybe even some MM locks (skb allocations?).

But even more "commonly used" consoles sometimes break that
expectation. E.g. 8250

serial8250_console_write()
serial8250_modem_status()
wake_up_interruptible()

And so on.

-ss