Re: [REGRESSION 5.8] x86/entry: DR0 break-on-write not working

2020-08-20 Thread peterz
On Wed, Aug 19, 2020 at 10:46:36PM -0500, Josh Poimboeuf wrote: > On Wed, Aug 19, 2020 at 05:14:18PM -0700, Andy Lutomirski wrote: > > I'm pretty sure you have the buggy sequence of events right, but for > > the wrong reason. There's nothing wrong with scheduling when > > delivering SIGTRAP, but

Re: [REGRESSION 5.8] x86/entry: DR0 break-on-write not working

2020-08-19 Thread Josh Poimboeuf
On Wed, Aug 19, 2020 at 05:14:18PM -0700, Andy Lutomirski wrote: > On Wed, Aug 19, 2020 at 3:47 PM Josh Poimboeuf wrote: > > What amazes me is that it successfully schedules back to the end of the > > #DB handler finish and everything keeps working. > > > > Do we not have assertions in the schedul

Re: [REGRESSION 5.8] x86/entry: DR0 break-on-write not working

2020-08-19 Thread Andy Lutomirski
On Wed, Aug 19, 2020 at 3:47 PM Josh Poimboeuf wrote: > > On Wed, Aug 19, 2020 at 11:35:34PM +0200, Peter Zijlstra wrote: > > On Wed, Aug 19, 2020 at 12:28:16PM -0700, Kyle Huey wrote: > > > > > > I'm guess that is not the expected outcome, is that the same failure you > > > > saw? > > > > > > Yes

Re: [REGRESSION 5.8] x86/entry: DR0 break-on-write not working

2020-08-19 Thread Josh Poimboeuf
On Wed, Aug 19, 2020 at 11:35:34PM +0200, Peter Zijlstra wrote: > On Wed, Aug 19, 2020 at 12:28:16PM -0700, Kyle Huey wrote: > > > > I'm guess that is not the expected outcome, is that the same failure you > > > saw? > > > > Yes. Is status also 0x4d00 for you? > > Indeed. > > > The program is e

Re: [REGRESSION 5.8] x86/entry: DR0 break-on-write not working

2020-08-19 Thread Peter Zijlstra
On Wed, Aug 19, 2020 at 12:28:16PM -0700, Kyle Huey wrote: > > I'm guess that is not the expected outcome, is that the same failure you > > saw? > > Yes. Is status also 0x4d00 for you? Indeed. > The program is expected to complete with no assertions firing. When I comment out the break-on-exec

Re: [REGRESSION 5.8] x86/entry: DR0 break-on-write not working

2020-08-19 Thread Kyle Huey
On Wed, Aug 19, 2020 at 11:42 AM wrote: > > On Wed, Aug 19, 2020 at 10:53:58AM -0700, Kyle Huey wrote: > > rr, a userspace record and replay debugger[0], has a test suite that > > attempts to exercise strange corners of the Linux API. One such > > test[1] began failing after 2bbc68f8373c0631ebf137

Re: [REGRESSION 5.8] x86/entry: DR0 break-on-write not working

2020-08-19 Thread peterz
On Wed, Aug 19, 2020 at 10:53:58AM -0700, Kyle Huey wrote: > rr, a userspace record and replay debugger[0], has a test suite that > attempts to exercise strange corners of the Linux API. One such > test[1] began failing after 2bbc68f8373c0631ebf137f376fbea00e8086be7. > I have not tried to understan

[REGRESSION 5.8] x86/entry: DR0 break-on-write not working

2020-08-19 Thread Kyle Huey
rr, a userspace record and replay debugger[0], has a test suite that attempts to exercise strange corners of the Linux API. One such test[1] began failing after 2bbc68f8373c0631ebf137f376fbea00e8086be7. I have not tried to understand what has changed in the kernel here but since the commit message