RE: [PATCH 2/2] futex, x86/mce: Avoid double machine checks

2021-01-08 Thread Luck, Tony
> Yeah, saw that, but that should be trivially fixable I'm thinking. Trivial, maybe ... but then follows the audit of other get_user() calls: git grep get_user\( | wc -l 2003 :-( -Tony

Re: [PATCH 2/2] futex, x86/mce: Avoid double machine checks

2021-01-08 Thread Peter Zijlstra
On Fri, Jan 08, 2021 at 11:08:58PM +, Luck, Tony wrote: > > I think this is horrid; why can't we have it return something different > > then -EFAULT instead? > > I did consider this ... but it appears that architectures aren't unified in > the > return value from get_user() But surely none

RE: [PATCH 2/2] futex, x86/mce: Avoid double machine checks

2021-01-08 Thread Luck, Tony
> I think this is horrid; why can't we have it return something different > then -EFAULT instead? I did consider this ... but it appears that architectures aren't unified in the return value from get_user() Here's another function involved in the futex call chain leading to this: static int

Re: [PATCH 2/2] futex, x86/mce: Avoid double machine checks

2021-01-08 Thread Peter Zijlstra
On Fri, Jan 08, 2021 at 02:22:51PM -0800, Tony Luck wrote: > futex_wait_setup() first tries to read the user value with page faults > disabled (because it holds a lock, and so cannot sleep). If that read > fails it drops the lock and tries again. > > But there are now two reasons why the user