Messages in this thread | | | Subject | Re: [RFC][PATCH 5/8] x86/mm: fix exception table comments | From | Sean Christopherson <> | Date | Mon, 10 Sep 2018 13:43:17 -0700 |
| |
On Fri, 2018-09-07 at 14:51 -0700, Dave Hansen wrote: > > > > > > > > + * Only do the expensive exception table search when we might be at > > > + * risk of a deadlock: > > > + * 1. We failed to acquire mmap_sem, and > > > + * 2. The access was an explicit kernel-mode access > > > + * (X86_PF_USER=0). > > Might be worth reminding the reader that X86_PF_USER will be set in > > sw_error_code for implicit accesses. I saw "explicit" and my mind > > immediately jumped to hw_error_code for whatever reason. E.g.: > > > > * 2. The access was an explicit kernel-mode access (we set X86_PF_USER > > * in sw_error_code for implicit kernel-mode accesses). > Yeah, that was not worded well. Is this better? > > > > > * Only do the expensive exception table search when we might be at > > * risk of a deadlock: > > * 1. We failed to acquire mmap_sem, and > > * 2. The access was an explicit kernel-mode access. An access > > * from user-mode will X86_PF_USER=1 set via hw_error_code or > > * set in sw_error_code if it were an implicit kernel-mode > > * access that originated in user mode.
For me, mentioning hw_error_code just muddies the waters, e.g. why is hw_error_code mentioned when it's not checked in the code? Comments alone won't help someone that's reading this code and doesn't understand that hardware sets X86_PF_USER for user-mode accesses. Maybe this?
* 2. The access was an explicit kernel-mode access. X86_PF_USER * is set in sw_error_code for both user-mode accesses and * implicit kernel-mode accesses that originated in user mode.
| |