kernel/git/stable/linux.git/mm/migrate.c, branch linux-4.19.y

mm/migrate: set swap entry values of THP tail pages properly.

2024-04-13T10:50:09+00:00

The tail pages in a THP can have swap entry information stored in their private field. When migrating to a new page, all tail pages of the new page need to update ->private to avoid future data corruption. This fix is stable-only, since after commit 07e09c483cbe ("mm/huge_memory: work on folio->swap instead of page->private when splitting folio"), subpages of a swapcached THP no longer requires the maintenance. Adding THPs to the swapcache was introduced in commit 38d8b4e6bdc87 ("mm, THP, swap: delay splitting THP during swap out"), where each subpage of a THP added to the swapcache had its own swapcache entry and required the ->private field to point to the correct swapcache entry. Later, when THP migration functionality was implemented in commit 616b8371539a6 ("mm: thp: enable thp migration in generic path"), it initially did not handle the subpages of swapcached THPs, failing to update their ->private fields or replace the subpage pointers in the swapcache. Subsequently, commit e71769ae5260 ("mm: enable thp migration for shmem thp") addressed the swapcache update aspect. This patch fixes the update of subpage ->private fields. Closes: https://lore.kernel.org/linux-mm/1707814102-22682-1-git-send-email-quic_charante@quicinc.com/ Fixes: 616b8371539a ("mm: thp: enable thp migration in generic path") Signed-off-by: Zi Yan Acked-by: David Hildenbrand Signed-off-by: Greg Kroah-Hartman

mm/migrate_device.c: flush TLB while holding PTL

2022-10-05T08:36:44+00:00

commit 60bae73708963de4a17231077285bd9ff2f41c44 upstream. When clearing a PTE the TLB should be flushed whilst still holding the PTL to avoid a potential race with madvise/munmap/etc. For example consider the following sequence: CPU0 CPU1 ---- ---- migrate_vma_collect_pmd() pte_unmap_unlock() madvise(MADV_DONTNEED) -> zap_pte_range() pte_offset_map_lock() [ PTE not present, TLB not flushed ] pte_unmap_unlock() [ page is still accessible via stale TLB ] flush_tlb_range() In this case the page may still be accessed via the stale TLB entry after madvise returns. Fix this by flushing the TLB while holding the PTL. Fixes: 8c3328f1f36a ("mm/migrate: migrate_vma() unmap page from vma while collecting pages") Link: https://lkml.kernel.org/r/9f801e9d8d830408f2ca27821f606e09aa856899.1662078528.git-series.apopple@nvidia.com Signed-off-by: Alistair Popple Reported-by: Nadav Amit Reviewed-by: "Huang, Ying" Acked-by: David Hildenbrand Acked-by: Peter Xu Cc: Alex Sierra Cc: Ben Skeggs Cc: Felix Kuehling Cc: huang ying Cc: Jason Gunthorpe Cc: John Hubbard Cc: Karol Herbst Cc: Logan Gunthorpe Cc: Lyude Paul Cc: Matthew Wilcox Cc: Paul Mackerras Cc: Ralph Campbell Cc: Signed-off-by: Andrew Morton Signed-off-by: Greg Kroah-Hartman

mm: fix dereference a null pointer in migrate[_huge]_page_move_mapping()

2022-03-23T08:10:42+00:00

Upstream doesn't use radix tree any more in migrate.c, no need this patch. The two functions look up a slot and dereference the pointer, If the pointer is null, the kernel would crash and dump. The 'numad' service calls 'migrate_pages' periodically. If some slots being replaced (Cache Eviction), the radix_tree_lookup_slot() returns a null pointer that causes kernel crash. "numad": crash> bt [exception RIP: migrate_page_move_mapping+337] Introduce pointer checking to avoid dereference a null pointer. Cc: # linux-4.19.y Signed-off-by: liqiong Signed-off-by: Greg Kroah-Hartman

mm: move_pages: report the number of non-attempted pages

2020-02-11T12:33:56+00:00

commit 5984fabb6e82d9ab4e6305cb99694c85d46de8ae upstream. Since commit a49bd4d71637 ("mm, numa: rework do_pages_move"), the semantic of move_pages() has changed to return the number of non-migrated pages if they were result of a non-fatal reasons (usually a busy page). This was an unintentional change that hasn't been noticed except for LTP tests which checked for the documented behavior. There are two ways to go around this change. We can even get back to the original behavior and return -EAGAIN whenever migrate_pages is not able to migrate pages due to non-fatal reasons. Another option would be to simply continue with the changed semantic and extend move_pages documentation to clarify that -errno is returned on an invalid input or when migration simply cannot succeed (e.g. -ENOMEM, -EBUSY) or the number of pages that couldn't have been migrated due to ephemeral reasons (e.g. page is pinned or locked for other reasons). This patch implements the second option because this behavior is in place for some time without anybody complaining and possibly new users depending on it. Also it allows to have a slightly easier error handling as the caller knows that it is worth to retry when err > 0. But since the new semantic would be aborted immediately if migration is failed due to ephemeral reasons, need include the number of non-attempted pages in the return value too. Link: http://lkml.kernel.org/r/1580160527-109104-1-git-send-email-yang.shi@linux.alibaba.com Fixes: a49bd4d71637 ("mm, numa: rework do_pages_move") Signed-off-by: Yang Shi Suggested-by: Michal Hocko Acked-by: Michal Hocko Reviewed-by: Wei Yang Cc: [4.17+] Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman

mm/migrate.c: also overwrite error when it is bigger than zero

2020-02-05T14:43:54+00:00

[ Upstream commit dfe9aa23cab7880a794db9eb2d176c00ed064eb6 ] If we get here after successfully adding page to list, err would be 1 to indicate the page is queued in the list. Current code has two problems: * on success, 0 is not returned * on error, if add_page_for_migratioin() return 1, and the following err1 from do_move_pages_to_node() is set, the err1 is not returned since err is 1 And these behaviors break the user interface. Link: http://lkml.kernel.org/r/20200119065753.21694-1-richardw.yang@linux.intel.com Fixes: e0153fc2c760 ("mm: move_pages: return valid node id in status if the page is already on the target node"). Signed-off-by: Wei Yang Acked-by: Yang Shi Cc: John Hubbard Cc: Vlastimil Babka Cc: Christoph Lameter Cc: Michal Hocko Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Sasha Levin

mm: move_pages: return valid node id in status if the page is already on the target node

2020-01-09T09:19:00+00:00

commit e0153fc2c7606f101392b682e720a7a456d6c766 upstream. Felix Abecassis reports move_pages() would return random status if the pages are already on the target node by the below test program: int main(void) { const long node_id = 1; const long page_size = sysconf(_SC_PAGESIZE); const int64_t num_pages = 8; unsigned long nodemask = 1 << node_id; long ret = set_mempolicy(MPOL_BIND, &nodemask, sizeof(nodemask)); if (ret < 0) return (EXIT_FAILURE); void **pages = malloc(sizeof(void*) * num_pages); for (int i = 0; i < num_pages; ++i) { pages[i] = mmap(NULL, page_size, PROT_WRITE | PROT_READ, MAP_PRIVATE | MAP_POPULATE | MAP_ANONYMOUS, -1, 0); if (pages[i] == MAP_FAILED) return (EXIT_FAILURE); } ret = set_mempolicy(MPOL_DEFAULT, NULL, 0); if (ret < 0) return (EXIT_FAILURE); int *nodes = malloc(sizeof(int) * num_pages); int *status = malloc(sizeof(int) * num_pages); for (int i = 0; i < num_pages; ++i) { nodes[i] = node_id; status[i] = 0xd0; /* simulate garbage values */ } ret = move_pages(0, num_pages, pages, nodes, status, MPOL_MF_MOVE); printf("move_pages: %ld\n", ret); for (int i = 0; i < num_pages; ++i) printf("status[%d] = %d\n", i, status[i]); } Then running the program would return nonsense status values: $ ./move_pages_bug move_pages: 0 status[0] = 208 status[1] = 208 status[2] = 208 status[3] = 208 status[4] = 208 status[5] = 208 status[6] = 208 status[7] = 208 This is because the status is not set if the page is already on the target node, but move_pages() should return valid status as long as it succeeds. The valid status may be errno or node id. We can't simply initialize status array to zero since the pages may be not on node 0. Fix it by updating status with node id which the page is already on. Link: http://lkml.kernel.org/r/1575584353-125392-1-git-send-email-yang.shi@linux.alibaba.com Fixes: a49bd4d71637 ("mm, numa: rework do_pages_move") Signed-off-by: Yang Shi Reported-by: Felix Abecassis Tested-by: Felix Abecassis Suggested-by: Michal Hocko Reviewed-by: John Hubbard Acked-by: Christoph Lameter Acked-by: Michal Hocko Reviewed-by: Vlastimil Babka Cc: Mel Gorman Cc: [4.17+] Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman

mm: thp: fix MADV_DONTNEED vs migrate_misplaced_transhuge_page race condition

2019-12-01T08:17:02+00:00

[ Upstream commit d7c3393413fe7e7dc54498ea200ea94742d61e18 ] Patch series "migrate_misplaced_transhuge_page race conditions". Aaron found a new instance of the THP MADV_DONTNEED race against pmdp_clear_flush* variants, that was apparently left unfixed. While looking into the race found by Aaron, I may have found two more issues in migrate_misplaced_transhuge_page. These race conditions would not cause kernel instability, but they'd corrupt userland data or leave data non zero after MADV_DONTNEED. I did only minor testing, and I don't expect to be able to reproduce this (especially the lack of ->invalidate_range before migrate_page_copy, requires the latest iommu hardware or infiniband to reproduce). The last patch is noop for x86 and it needs further review from maintainers of archs that implement flush_cache_range() (not in CC yet). To avoid confusion, it's not the first patch that introduces the bug fixed in the second patch, even before removing the pmdp_huge_clear_flush_notify, that _notify suffix was called after migrate_page_copy already run. This patch (of 3): This is a corollary of ced108037c2aa ("thp: fix MADV_DONTNEED vs. numa balancing race"), 58ceeb6bec8 ("thp: fix MADV_DONTNEED vs. MADV_FREE race") and 5b7abeae3af8c ("thp: fix MADV_DONTNEED vs clear soft dirty race). When the above three fixes where posted Dave asked https://lkml.kernel.org/r/929b3844-aec2-0111-fef7-8002f9d4e2b9@intel.com but apparently this was missed. The pmdp_clear_flush* in migrate_misplaced_transhuge_page() was introduced in a54a407fbf7 ("mm: Close races between THP migration and PMD numa clearing"). The important part of such commit is only the part where the page lock is not released until the first do_huge_pmd_numa_page() finished disarming the pagenuma/protnone. The addition of pmdp_clear_flush() wasn't beneficial to such commit and there's no commentary about such an addition either. I guess the pmdp_clear_flush() in such commit was added just in case for safety, but it ended up introducing the MADV_DONTNEED race condition found by Aaron. At that point in time nobody thought of such kind of MADV_DONTNEED race conditions yet (they were fixed later) so the code may have looked more robust by adding the pmdp_clear_flush(). This specific race condition won't destabilize the kernel, but it can confuse userland because after MADV_DONTNEED the memory won't be zeroed out. This also optimizes the code and removes a superfluous TLB flush. [akpm@linux-foundation.org: reflow comment to 80 cols, fix grammar and typo (beacuse)] Link: http://lkml.kernel.org/r/20181013002430.698-2-aarcange@redhat.com Signed-off-by: Andrea Arcangeli Reported-by: Aaron Tomlin Acked-by: Mel Gorman Acked-by: Kirill A. Shutemov Cc: Jerome Glisse Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Sasha Levin

mm/migrate.c: initialize pud_entry in migrate_vma()

2019-09-16T06:22:22+00:00

[ Upstream commit 7b358c6f12dc82364f6d317f8c8f1d794adbc3f5 ] When CONFIG_MIGRATE_VMA_HELPER is enabled, migrate_vma() calls migrate_vma_collect() which initializes a struct mm_walk but didn't initialize mm_walk.pud_entry. (Found by code inspection) Use a C structure initialization to make sure it is set to NULL. Link: http://lkml.kernel.org/r/20190719233225.12243-1-rcampbell@nvidia.com Fixes: 8763cb45ab967 ("mm/migrate: new memory migration helper for use with device memory") Signed-off-by: Ralph Campbell Reviewed-by: John Hubbard Reviewed-by: Andrew Morton Cc: "Jérôme Glisse" Cc: Mel Gorman Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Sasha Levin

mm/migrate.c: add missing flush_dcache_page for non-mapped page migrate

2019-04-03T04:26:28+00:00

commit d2b2c6dd227ba5b8a802858748ec9a780cb75b47 upstream. Our MIPS 1004Kc SoCs were seeing random userspace crashes with SIGILL and SIGSEGV that could not be traced back to a userspace code bug. They had all the magic signs of an I/D cache coherency issue. Now recently we noticed that the /proc/sys/vm/compact_memory interface was quite efficient at provoking this class of userspace crashes. Studying the code in mm/migrate.c there is a distinction made between migrating a page that is mapped at the instant of migration and one that is not mapped. Our problem turned out to be the non-mapped pages. For the non-mapped page the code performs a copy of the page content and all relevant meta-data of the page without doing the required D-cache maintenance. This leaves dirty data in the D-cache of the CPU and on the 1004K cores this data is not visible to the I-cache. A subsequent page-fault that triggers a mapping of the page will happily serve the process with potentially stale code. What about ARM then, this bug should have seen greater exposure? Well ARM became immune to this flaw back in 2010, see commit c01778001a4f ("ARM: 6379/1: Assume new page cache pages have dirty D-cache"). My proposed fix moves the D-cache maintenance inside move_to_new_page to make it common for both cases. Link: http://lkml.kernel.org/r/20190315083502.11849-1-larper@axis.com Fixes: 97ee0524614 ("flush cache before installing new page at migraton") Signed-off-by: Lars Persson Reviewed-by: Paul Burton Acked-by: Mel Gorman Cc: Ralf Baechle Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman

hugetlbfs: fix races and page leaks during migration

2019-03-05T16:58:53+00:00

commit cb6acd01e2e43fd8bad11155752b7699c3d0fb76 upstream. hugetlb pages should only be migrated if they are 'active'. The routines set/clear_page_huge_active() modify the active state of hugetlb pages. When a new hugetlb page is allocated at fault time, set_page_huge_active is called before the page is locked. Therefore, another thread could race and migrate the page while it is being added to page table by the fault code. This race is somewhat hard to trigger, but can be seen by strategically adding udelay to simulate worst case scheduling behavior. Depending on 'how' the code races, various BUG()s could be triggered. To address this issue, simply delay the set_page_huge_active call until after the page is successfully added to the page table. Hugetlb pages can also be leaked at migration time if the pages are associated with a file in an explicitly mounted hugetlbfs filesystem. For example, consider a two node system with 4GB worth of huge pages available. A program mmaps a 2G file in a hugetlbfs filesystem. It then migrates the pages associated with the file from one node to another. When the program exits, huge page counts are as follows: node0 1024 free_hugepages 1024 nr_hugepages node1 0 free_hugepages 1024 nr_hugepages Filesystem Size Used Avail Use% Mounted on nodev 4.0G 2.0G 2.0G 50% /var/opt/hugepool That is as expected. 2G of huge pages are taken from the free_hugepages counts, and 2G is the size of the file in the explicitly mounted filesystem. If the file is then removed, the counts become: node0 1024 free_hugepages 1024 nr_hugepages node1 1024 free_hugepages 1024 nr_hugepages Filesystem Size Used Avail Use% Mounted on nodev 4.0G 2.0G 2.0G 50% /var/opt/hugepool Note that the filesystem still shows 2G of pages used, while there actually are no huge pages in use. The only way to 'fix' the filesystem accounting is to unmount the filesystem If a hugetlb page is associated with an explicitly mounted filesystem, this information in contained in the page_private field. At migration time, this information is not preserved. To fix, simply transfer page_private from old to new page at migration time if necessary. There is a related race with removing a huge page from a file and migration. When a huge page is removed from the pagecache, the page_mapping() field is cleared, yet page_private remains set until the page is actually freed by free_huge_page(). A page could be migrated while in this state. However, since page_mapping() is not set the hugetlbfs specific routine to transfer page_private is not called and we leak the page count in the filesystem. To fix that, check for this condition before migrating a huge page. If the condition is detected, return EBUSY for the page. Link: http://lkml.kernel.org/r/74510272-7319-7372-9ea6-ec914734c179@oracle.com Link: http://lkml.kernel.org/r/20190212221400.3512-1-mike.kravetz@oracle.com Fixes: bcc54222309c ("mm: hugetlb: introduce page_huge_active") Signed-off-by: Mike Kravetz Reviewed-by: Naoya Horiguchi Cc: Michal Hocko Cc: Andrea Arcangeli Cc: "Kirill A . Shutemov" Cc: Mel Gorman Cc: Davidlohr Bueso Cc: [mike.kravetz@oracle.com: v2] Link: http://lkml.kernel.org/r/7534d322-d782-8ac6-1c8d-a8dc380eb3ab@oracle.com [mike.kravetz@oracle.com: update comment and changelog] Link: http://lkml.kernel.org/r/420bcfd6-158b-38e4-98da-26d0cd85bd01@oracle.com Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman