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Yes. Like, serious data corruption would be avoidable. > > But usually we're already pretty screwed if the thing happened right? So > it's rare if ever that this would be legit? > > Linus's point of view is that we shouldn't use them _at all_ right? So > maybe even this situation isn't one where we'd want to use one? I think the grey zone is actual data corruption. But one has to have a pretty good reason to use a BUG_ON and not a WARN_ON_ONCE() + recovery. > >> >> While at it, let's just convert all VM_BUG_ON to VM_WARN_ON_ONCE as >> well. Add one comment for the pfn_valid() check. > > Yeah VM_BUG_ON() is just _weird_. Maybe we should get rid of all of them > full stop? That's my thinking a well. > >> >> We have to introduce VM_WARN_ON_ONCE_VMA() to make that fly. > > I checked the implementation vs. the other VM_WARN_ON_ONCE_*()'s and it > looks good. > > I wonder if we can find a way to not duplicate this code... but one for a > follow up I think :>) > >> >> Drop the BUG_ON after mmap_read_lock_killable(), if that ever returns >> something > 0 we're in bigger trouble. Convert the other BUG_ON's into >> VM_WARN_ON_ONCE as well, they are in a similar domain "should never >> happen", but more reasonable to check for during early testing. >> >> Cc: Andrew Morton >> Cc: Lorenzo Stoakes >> Cc: "Liam R. Howlett" >> Cc: Vlastimil Babka >> Cc: Mike Rapoport >> Cc: Suren Baghdasaryan >> Cc: Michal Hocko >> Cc: Jason Gunthorpe >> Cc: John Hubbard >> Cc: Peter Xu >> Signed-off-by: David Hildenbrand > > LGTM so, > > Reviewed-by: Lorenzo Stoakes > > Thanks! > One nit below. > >> --- >> >> Wanted to do this for a long time, but my todo list keeps growing ... > > Sounds familiar :) Merge window a chance to do some of these things... > >> >> Based on mm/mm-unstable >> >> --- >> include/linux/mmdebug.h | 12 ++++++++++++ >> mm/gup.c | 41 +++++++++++++++++++---------------------- >> 2 files changed, 31 insertions(+), 22 deletions(-) >> >> diff --git a/include/linux/mmdebug.h b/include/linux/mmdebug.h >> index a0a3894900ed4..14a45979cccc9 100644 >> --- a/include/linux/mmdebug.h >> +++ b/include/linux/mmdebug.h >> @@ -89,6 +89,17 @@ void vma_iter_dump_tree(const struct vma_iterator *vmi); >> } \ >> unlikely(__ret_warn_once); \ >> }) >> +#define VM_WARN_ON_ONCE_VMA(cond, vma) ({ \ >> + static bool __section(".data..once") __warned; \ >> + int __ret_warn_once = !!(cond); \ >> + \ >> + if (unlikely(__ret_warn_once && !__warned)) { \ >> + dump_vma(vma); \ >> + __warned = true; \ >> + WARN_ON(1); \ >> + } \ >> + unlikely(__ret_warn_once); \ >> +}) > > An aside, I wonder if we could somehow make this generic for various > WARN_ON_ONCE()'s? Yeah, probably. Maybe it will get .... ugly :) > >> #define VM_WARN_ON_VMG(cond, vmg) ({ \ >> int __ret_warn = !!(cond); \ >> \ >> @@ -115,6 +126,7 @@ void vma_iter_dump_tree(const struct vma_iterator *vmi); >> #define VM_WARN_ON_FOLIO(cond, folio) BUILD_BUG_ON_INVALID(cond) >> #define VM_WARN_ON_ONCE_FOLIO(cond, folio) BUILD_BUG_ON_INVALID(cond) >> #define VM_WARN_ON_ONCE_MM(cond, mm) BUILD_BUG_ON_INVALID(cond) >> +#define VM_WARN_ON_ONCE_VMA(cond, vma) BUILD_BUG_ON_INVALID(cond) >> #define VM_WARN_ON_VMG(cond, vmg) BUILD_BUG_ON_INVALID(cond) >> #define VM_WARN_ONCE(cond, format...) BUILD_BUG_ON_INVALID(cond) >> #define VM_WARN(cond, format...) BUILD_BUG_ON_INVALID(cond) >> diff --git a/mm/gup.c b/mm/gup.c >> index e065a49842a87..3c3931fcdd820 100644 >> --- a/mm/gup.c >> +++ b/mm/gup.c >> @@ -64,11 +64,11 @@ static inline void sanity_check_pinned_pages(struct page **pages, >> !folio_test_anon(folio)) >> continue; >> if (!folio_test_large(folio) || folio_test_hugetlb(folio)) >> - VM_BUG_ON_PAGE(!PageAnonExclusive(&folio->page), page); >> + VM_WARN_ON_ONCE_PAGE(!PageAnonExclusive(&folio->page), page); >> else >> /* Either a PTE-mapped or a PMD-mapped THP. */ >> - VM_BUG_ON_PAGE(!PageAnonExclusive(&folio->page) && >> - !PageAnonExclusive(page), page); >> + VM_WARN_ON_ONCE_PAGE(!PageAnonExclusive(&folio->page) && >> + !PageAnonExclusive(page), page); > > Nit but wouldn't VM_WARN_ON_ONCE_FOLIO() work better here? No, we want the actual problematic page here, as that can give us clues what is going wrong. For the small-folio case above we could use it, though. -- Cheers, David / dhildenb