On 10.10.19 02:26, Naoya Horiguchi wrote: > On Wed, Oct 09, 2019 at 04:24:35PM +0200, David Hildenbrand wrote: >> We should check for pfn_to_online_page() to not access uninitialized >> memmaps. Reshuffle the code so we don't have to duplicate the error >> message. >> >> Cc: Naoya Horiguchi <[email protected]> >> Cc: Andrew Morton <[email protected]> >> Cc: Michal Hocko <[email protected]> >> Signed-off-by: David Hildenbrand <[email protected]> >> --- >> mm/memory-failure.c | 14 ++++++++------ >> 1 file changed, 8 insertions(+), 6 deletions(-) >> >> diff --git a/mm/memory-failure.c b/mm/memory-failure.c >> index 7ef849da8278..e866e6e5660b 100644 >> --- a/mm/memory-failure.c >> +++ b/mm/memory-failure.c >> @@ -1253,17 +1253,19 @@ int memory_failure(unsigned long pfn, int flags) >> if (!sysctl_memory_failure_recovery) >> panic("Memory failure on page %lx", pfn); >> >> - if (!pfn_valid(pfn)) { >> + p = pfn_to_online_page(pfn); >> + if (!p) { >> + if (pfn_valid(pfn)) { >> + pgmap = get_dev_pagemap(pfn, NULL); >> + if (pgmap) >> + return memory_failure_dev_pagemap(pfn, flags, >> + pgmap); >> + } >> pr_err("Memory failure: %#lx: memory outside kernel control\n", >> pfn); >> return -ENXIO; >> } >> >> - pgmap = get_dev_pagemap(pfn, NULL); >> - if (pgmap) >> - return memory_failure_dev_pagemap(pfn, flags, pgmap); >> - >> - p = pfn_to_page(pfn); > > This change seems to assume that memory_failure_dev_pagemap() is never > called for online pages. Is it an intended behavior? > Or the concept "online pages" is not applicable to zone device pages?
Yes, that's the real culprit. ZONE_DEVICE/devmem pages are never online (SECTION_IS_ONLINE). The terminology "online" only applies to pages that were given to the buddy. And as we support sup-section hotadd for devmem, we cannot easily make use of the section flag it. I already proposed somewhere to convert SECTION_IS_ONLINE to a subsection bitmap and call it something like pfn_active(). pfn_online() would then be "pfn_active() && zone != ZONE_DEVICE". And we could use pfn_active() everywhere to test for initialized memmaps (well, besides some special cases like device reserved memory that does not span full sub-sections). Until now, nobody volunteered and I have other things to do. -- Thanks, David / dhildenb
