| Message ID | alpine.LSU.2.11.1805291841070.3197@eggly.anvils (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On 30.05.2018 04:50, Hugh Dickins wrote: > Swapping load on huge=always tmpfs (with khugepaged tuned up to be very > eager, but I'm not sure that is relevant) soon hung uninterruptibly, > waiting for page lock in shmem_getpage_gfp()'s find_lock_entry(), most > often when "cp -a" was trying to write to a smallish file. Debug showed > that the page in question was not locked, and page->mapping NULL by now, > but page->index consistent with having been in a huge page before. > > Reproduced in minutes on a 4.15 kernel, even with 4.17's 605ca5ede764 > ("mm/huge_memory.c: reorder operations in __split_huge_page_tail()") > added in; but took hours to reproduce on a 4.17 kernel (no idea why). > > The culprit proved to be the __ClearPageDirty() on tails beyond i_size > in __split_huge_page(): the non-atomic __bitoperation may have been safe > when 4.8's baa355fd3314 ("thp: file pages support for split_huge_page()") > introduced it, but liable to erase PageWaiters after 4.10's 62906027091f > ("mm: add PageWaiters indicating tasks are waiting for a page bit"). > > Fixes: 62906027091f ("mm: add PageWaiters indicating tasks are waiting for a page bit") > Signed-off-by: Hugh Dickins <hughd@google.com> > --- > > It's not a 4.17-rc regression that this fixes, so no great need to slip > this into 4.17 at the last moment - though it makes a good companion to > Konstantin's 605ca5ede764. I think they both should go to stable, but > since Konstantin's already went into rc1 without that tag, we shall > have to recommend Konstantin's to GregKH out-of-band. Good catch. This is the same issue, so all 4.10+ needs them both. Preserving known regressions in core pieces like lock_page() is a bad idea. > > mm/huge_memory.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > --- 4.17-rc7/mm/huge_memory.c 2018-04-26 10:48:36.019288258 -0700 > +++ linux/mm/huge_memory.c 2018-05-29 18:14:52.095512715 -0700 > @@ -2431,7 +2431,7 @@ static void __split_huge_page(struct pag > __split_huge_page_tail(head, i, lruvec, list); > /* Some pages can be beyond i_size: drop them from page cache */ > if (head[i].index >= end) { > - __ClearPageDirty(head + i); > + ClearPageDirty(head + i); > __delete_from_page_cache(head + i, NULL); > if (IS_ENABLED(CONFIG_SHMEM) && PageSwapBacked(head)) > shmem_uncharge(head->mapping->host, 1); >
On Wed, May 30, 2018 at 01:50:22AM +0000, Hugh Dickins wrote: > Swapping load on huge=always tmpfs (with khugepaged tuned up to be very > eager, but I'm not sure that is relevant) soon hung uninterruptibly, > waiting for page lock in shmem_getpage_gfp()'s find_lock_entry(), most > often when "cp -a" was trying to write to a smallish file. Debug showed > that the page in question was not locked, and page->mapping NULL by now, > but page->index consistent with having been in a huge page before. > > Reproduced in minutes on a 4.15 kernel, even with 4.17's 605ca5ede764 > ("mm/huge_memory.c: reorder operations in __split_huge_page_tail()") > added in; but took hours to reproduce on a 4.17 kernel (no idea why). > > The culprit proved to be the __ClearPageDirty() on tails beyond i_size > in __split_huge_page(): the non-atomic __bitoperation may have been safe > when 4.8's baa355fd3314 ("thp: file pages support for split_huge_page()") > introduced it, but liable to erase PageWaiters after 4.10's 62906027091f > ("mm: add PageWaiters indicating tasks are waiting for a page bit"). > > Fixes: 62906027091f ("mm: add PageWaiters indicating tasks are waiting for a page bit") > Signed-off-by: Hugh Dickins <hughd@google.com> Thanks for catching this. Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
--- 4.17-rc7/mm/huge_memory.c 2018-04-26 10:48:36.019288258 -0700 +++ linux/mm/huge_memory.c 2018-05-29 18:14:52.095512715 -0700 @@ -2431,7 +2431,7 @@ static void __split_huge_page(struct pag __split_huge_page_tail(head, i, lruvec, list); /* Some pages can be beyond i_size: drop them from page cache */ if (head[i].index >= end) { - __ClearPageDirty(head + i); + ClearPageDirty(head + i); __delete_from_page_cache(head + i, NULL); if (IS_ENABLED(CONFIG_SHMEM) && PageSwapBacked(head)) shmem_uncharge(head->mapping->host, 1);
Swapping load on huge=always tmpfs (with khugepaged tuned up to be very eager, but I'm not sure that is relevant) soon hung uninterruptibly, waiting for page lock in shmem_getpage_gfp()'s find_lock_entry(), most often when "cp -a" was trying to write to a smallish file. Debug showed that the page in question was not locked, and page->mapping NULL by now, but page->index consistent with having been in a huge page before. Reproduced in minutes on a 4.15 kernel, even with 4.17's 605ca5ede764 ("mm/huge_memory.c: reorder operations in __split_huge_page_tail()") added in; but took hours to reproduce on a 4.17 kernel (no idea why). The culprit proved to be the __ClearPageDirty() on tails beyond i_size in __split_huge_page(): the non-atomic __bitoperation may have been safe when 4.8's baa355fd3314 ("thp: file pages support for split_huge_page()") introduced it, but liable to erase PageWaiters after 4.10's 62906027091f ("mm: add PageWaiters indicating tasks are waiting for a page bit"). Fixes: 62906027091f ("mm: add PageWaiters indicating tasks are waiting for a page bit") Signed-off-by: Hugh Dickins <hughd@google.com> --- It's not a 4.17-rc regression that this fixes, so no great need to slip this into 4.17 at the last moment - though it makes a good companion to Konstantin's 605ca5ede764. I think they both should go to stable, but since Konstantin's already went into rc1 without that tag, we shall have to recommend Konstantin's to GregKH out-of-band. mm/huge_memory.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)