diff options
| author | Mark Rutland <mark.rutland@arm.com> | 2017-06-16 14:02:34 -0700 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2017-07-05 14:40:19 +0200 |
| commit | 2aa6d036b716c9242222e054d4ef34905ad45fd3 (patch) | |
| tree | 858830a4a379cbe2960f3a78ef9393ec315a13ad /mm | |
| parent | 08cb8e5f83fd2d4f6327173cc01322bc842806f1 (diff) | |
mm: numa: avoid waiting on freed migrated pages
commit 3c226c637b69104f6b9f1c6ec5b08d7b741b3229 upstream.
In do_huge_pmd_numa_page(), we attempt to handle a migrating thp pmd by
waiting until the pmd is unlocked before we return and retry. However,
we can race with migrate_misplaced_transhuge_page():
// do_huge_pmd_numa_page // migrate_misplaced_transhuge_page()
// Holds 0 refs on page // Holds 2 refs on page
vmf->ptl = pmd_lock(vma->vm_mm, vmf->pmd);
/* ... */
if (pmd_trans_migrating(*vmf->pmd)) {
page = pmd_page(*vmf->pmd);
spin_unlock(vmf->ptl);
ptl = pmd_lock(mm, pmd);
if (page_count(page) != 2)) {
/* roll back */
}
/* ... */
mlock_migrate_page(new_page, page);
/* ... */
spin_unlock(ptl);
put_page(page);
put_page(page); // page freed here
wait_on_page_locked(page);
goto out;
}
This can result in the freed page having its waiters flag set
unexpectedly, which trips the PAGE_FLAGS_CHECK_AT_PREP checks in the
page alloc/free functions. This has been observed on arm64 KVM guests.
We can avoid this by having do_huge_pmd_numa_page() take a reference on
the page before dropping the pmd lock, mirroring what we do in
__migration_entry_wait().
When we hit the race, migrate_misplaced_transhuge_page() will see the
reference and abort the migration, as it may do today in other cases.
Fixes: b8916634b77bffb2 ("mm: Prevent parallel splits during THP migration")
Link: http://lkml.kernel.org/r/1497349722-6731-2-git-send-email-will.deacon@arm.com
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Acked-by: Steve Capper <steve.capper@arm.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Mel Gorman <mgorman@suse.de>
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 | 6 |
1 files changed, 6 insertions, 0 deletions
diff --git a/mm/huge_memory.c b/mm/huge_memory.c index d5b2b759f76f..e7d5db958538 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -1227,8 +1227,11 @@ int do_huge_pmd_numa_page(struct fault_env *fe, pmd_t pmd) */ if (unlikely(pmd_trans_migrating(*fe->pmd))) { page = pmd_page(*fe->pmd); + if (!get_page_unless_zero(page)) + goto out_unlock; spin_unlock(fe->ptl); wait_on_page_locked(page); + put_page(page); goto out; } @@ -1260,8 +1263,11 @@ int do_huge_pmd_numa_page(struct fault_env *fe, pmd_t pmd) /* Migration could have started since the pmd_trans_migrating check */ if (!page_locked) { + if (!get_page_unless_zero(page)) + goto out_unlock; spin_unlock(fe->ptl); wait_on_page_locked(page); + put_page(page); page_nid = -1; goto out; } |