| Message ID | 20180824192549.30844-3-jglisse@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | HMM updates, improvements and fixes | expand |
On Fri, Aug 24, 2018 at 03:25:44PM -0400, jglisse@redhat.com wrote: > From: Ralph Campbell <rcampbell@nvidia.com> > > Private ZONE_DEVICE pages use a special pte entry and thus are not > present. Properly handle this case in map_pte(), it is already handled > in check_pte(), the map_pte() part was lost in some rebase most probably. > > Without this patch the slow migration path can not migrate back private > ZONE_DEVICE memory to regular memory. This was found after stress > testing migration back to system memory. This ultimatly can lead the > CPU to an infinite page fault loop on the special swap entry. > > Signed-off-by: Ralph Campbell <rcampbell@nvidia.com> > Signed-off-by: Jérôme Glisse <jglisse@redhat.com> > Cc: Andrew Morton <akpm@linux-foundation.org> > Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> > Cc: stable@vger.kernel.org > --- > mm/page_vma_mapped.c | 9 +++++++++ > 1 file changed, 9 insertions(+) > > diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c > index ae3c2a35d61b..1cf5b9bfb559 100644 > --- a/mm/page_vma_mapped.c > +++ b/mm/page_vma_mapped.c > @@ -21,6 +21,15 @@ static bool map_pte(struct page_vma_mapped_walk *pvmw) > if (!is_swap_pte(*pvmw->pte)) > return false; > } else { > + if (is_swap_pte(*pvmw->pte)) { > + swp_entry_t entry; > + > + /* Handle un-addressable ZONE_DEVICE memory */ > + entry = pte_to_swp_entry(*pvmw->pte); > + if (is_device_private_entry(entry)) > + return true; > + } > + This happens just for !PVMW_SYNC && PVMW_MIGRATION? I presume this is triggered via the remove_migration_pte() code path? Doesn't returning true here imply that we've taken the ptl lock for the pvmw? Balbir
On Fri, Aug 31, 2018 at 12:05:38AM +1000, Balbir Singh wrote: > On Fri, Aug 24, 2018 at 03:25:44PM -0400, jglisse@redhat.com wrote: > > From: Ralph Campbell <rcampbell@nvidia.com> > > > > Private ZONE_DEVICE pages use a special pte entry and thus are not > > present. Properly handle this case in map_pte(), it is already handled > > in check_pte(), the map_pte() part was lost in some rebase most probably. > > > > Without this patch the slow migration path can not migrate back private > > ZONE_DEVICE memory to regular memory. This was found after stress > > testing migration back to system memory. This ultimatly can lead the > > CPU to an infinite page fault loop on the special swap entry. > > > > Signed-off-by: Ralph Campbell <rcampbell@nvidia.com> > > Signed-off-by: Jérôme Glisse <jglisse@redhat.com> > > Cc: Andrew Morton <akpm@linux-foundation.org> > > Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> > > Cc: stable@vger.kernel.org > > --- > > mm/page_vma_mapped.c | 9 +++++++++ > > 1 file changed, 9 insertions(+) > > > > diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c > > index ae3c2a35d61b..1cf5b9bfb559 100644 > > --- a/mm/page_vma_mapped.c > > +++ b/mm/page_vma_mapped.c > > @@ -21,6 +21,15 @@ static bool map_pte(struct page_vma_mapped_walk *pvmw) > > if (!is_swap_pte(*pvmw->pte)) > > return false; > > } else { > > + if (is_swap_pte(*pvmw->pte)) { > > + swp_entry_t entry; > > + > > + /* Handle un-addressable ZONE_DEVICE memory */ > > + entry = pte_to_swp_entry(*pvmw->pte); > > + if (is_device_private_entry(entry)) > > + return true; > > + } > > + > > This happens just for !PVMW_SYNC && PVMW_MIGRATION? I presume this > is triggered via the remove_migration_pte() code path? Doesn't > returning true here imply that we've taken the ptl lock for the > pvmw? This happens through try_to_unmap() from migrate_vma_unmap() and thus has !PVMW_SYNC and !PVMW_MIGRATION But you are right about the ptl lock, so looking at code we were just doing pte modification without holding the pte lock but the page_vma_mapped_walk() would not try to unlock as pvmw->ptl == NULL so this never triggered any warning. I am gonna post a v2 shortly which address that. Cheers, Jérôme
diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c index ae3c2a35d61b..1cf5b9bfb559 100644 --- a/mm/page_vma_mapped.c +++ b/mm/page_vma_mapped.c @@ -21,6 +21,15 @@ static bool map_pte(struct page_vma_mapped_walk *pvmw) if (!is_swap_pte(*pvmw->pte)) return false; } else { + if (is_swap_pte(*pvmw->pte)) { + swp_entry_t entry; + + /* Handle un-addressable ZONE_DEVICE memory */ + entry = pte_to_swp_entry(*pvmw->pte); + if (is_device_private_entry(entry)) + return true; + } + if (!pte_present(*pvmw->pte)) return false; }