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author | Hugh Dickins <hughd@google.com> | 2021-02-05 05:32:31 +0300 |
---|---|---|
committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2021-02-10 11:29:21 +0300 |
commit | 0a249ac189fc7fad3e989640384fde5fe62ac550 (patch) | |
tree | a5991d9bec404f9b966af2f78c03b3a3d4151b98 /mm | |
parent | 9abdd2c05b59ad6f0ab4aaa3977c544c52d56f8a (diff) | |
download | linux-0a249ac189fc7fad3e989640384fde5fe62ac550.tar.xz |
mm: thp: fix MADV_REMOVE deadlock on shmem THP
commit 1c2f67308af4c102b4e1e6cd6f69819ae59408e0 upstream.
Sergey reported deadlock between kswapd correctly doing its usual
lock_page(page) followed by down_read(page->mapping->i_mmap_rwsem), and
madvise(MADV_REMOVE) on an madvise(MADV_HUGEPAGE) area doing
down_write(page->mapping->i_mmap_rwsem) followed by lock_page(page).
This happened when shmem_fallocate(punch hole)'s unmap_mapping_range()
reaches zap_pmd_range()'s call to __split_huge_pmd(). The same deadlock
could occur when partially truncating a mapped huge tmpfs file, or using
fallocate(FALLOC_FL_PUNCH_HOLE) on it.
__split_huge_pmd()'s page lock was added in 5.8, to make sure that any
concurrent use of reuse_swap_page() (holding page lock) could not catch
the anon THP's mapcounts and swapcounts while they were being split.
Fortunately, reuse_swap_page() is never applied to a shmem or file THP
(not even by khugepaged, which checks PageSwapCache before calling), and
anonymous THPs are never created in shmem or file areas: so that
__split_huge_pmd()'s page lock can only be necessary for anonymous THPs,
on which there is no risk of deadlock with i_mmap_rwsem.
Link: https://lkml.kernel.org/r/alpine.LSU.2.11.2101161409470.2022@eggly.anvils
Fixes: c444eb564fb1 ("mm: thp: make the THP mapcount atomic against __split_huge_pmd_locked()")
Signed-off-by: Hugh Dickins <hughd@google.com>
Reported-by: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Reviewed-by: Andrea Arcangeli <aarcange@redhat.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'mm')
-rw-r--r-- | mm/huge_memory.c | 37 |
1 files changed, 23 insertions, 14 deletions
diff --git a/mm/huge_memory.c b/mm/huge_memory.c index 85eda66eb625..4a78514830d5 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -2188,7 +2188,7 @@ void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd, { spinlock_t *ptl; struct mmu_notifier_range range; - bool was_locked = false; + bool do_unlock_page = false; pmd_t _pmd; mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, vma, vma->vm_mm, @@ -2204,7 +2204,6 @@ void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd, VM_BUG_ON(freeze && !page); if (page) { VM_WARN_ON_ONCE(!PageLocked(page)); - was_locked = true; if (page != pmd_page(*pmd)) goto out; } @@ -2213,19 +2212,29 @@ repeat: if (pmd_trans_huge(*pmd)) { if (!page) { page = pmd_page(*pmd); - if (unlikely(!trylock_page(page))) { - get_page(page); - _pmd = *pmd; - spin_unlock(ptl); - lock_page(page); - spin_lock(ptl); - if (unlikely(!pmd_same(*pmd, _pmd))) { - unlock_page(page); + /* + * An anonymous page must be locked, to ensure that a + * concurrent reuse_swap_page() sees stable mapcount; + * but reuse_swap_page() is not used on shmem or file, + * and page lock must not be taken when zap_pmd_range() + * calls __split_huge_pmd() while i_mmap_lock is held. + */ + if (PageAnon(page)) { + if (unlikely(!trylock_page(page))) { + get_page(page); + _pmd = *pmd; + spin_unlock(ptl); + lock_page(page); + spin_lock(ptl); + if (unlikely(!pmd_same(*pmd, _pmd))) { + unlock_page(page); + put_page(page); + page = NULL; + goto repeat; + } put_page(page); - page = NULL; - goto repeat; } - put_page(page); + do_unlock_page = true; } } if (PageMlocked(page)) @@ -2235,7 +2244,7 @@ repeat: __split_huge_pmd_locked(vma, pmd, range.start, freeze); out: spin_unlock(ptl); - if (!was_locked && page) + if (do_unlock_page) unlock_page(page); /* * No need to double call mmu_notifier->invalidate_range() callback. |