On 08/25/2017 03:02 PM, Nadav Amit wrote: > Michal Hocko <mhocko@xxxxxxxxxx> wrote: > >> Hmm, I do not see this neither in linux-mm nor LKML. Strange >> >> On Wed 23-08-17 14:41:21, Andrew Morton wrote: >>> From: Eric Biggers <ebiggers@xxxxxxxxxx> >>> Subject: mm/madvise.c: fix freeing of locked page with MADV_FREE >>> >>> If madvise(..., MADV_FREE) split a transparent hugepage, it called >>> put_page() before unlock_page(). This was wrong because put_page() can >>> free the page, e.g. if a concurrent madvise(..., MADV_DONTNEED) has >>> removed it from the memory mapping. put_page() then rightfully complained >>> about freeing a locked page. >>> >>> Fix this by moving the unlock_page() before put_page(). > > Quick grep shows that a similar flow (put_page() followed by an > unlock_page() ) also happens in hugetlbfs_fallocate(). Isn’t it a problem as > well? I assume you are asking about this block of code? /* * page_put due to reference from alloc_huge_page() * unlock_page because locked by add_to_page_cache() */ put_page(page); unlock_page(page); Well, there is a typo (page_put) in the comment. :( However, in this case we have just added the huge page to a hugetlbfs file. The put_page() is there just to drop the reference count on the page (taken when allocated). It will still be non-zero as we have successfully added it to the page cache. So, we are not freeing the page here, just dropping the reference count. This should not cause a problem like that seen in madvise. -- Mike Kravetz -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx"> email@xxxxxxxxx </a>