[PATCH v3 5/8] mm: make folio_lock_fault indicate the state of mmap_lock upon return

Suren Baghdasaryan
2023-06-27T04:23:39Z

folio_lock_fault might drop mmap_lock before returning and to extend it
to work with per-VMA locks, the callers will need to know whether the
lock was dropped or is still held. Introduce new fault_flag to indicate
whether the lock got dropped and store it inside vm_fault flags.

Signed-off-by: Suren Baghdasaryan <surenb@google.com>
---
include/linux/mm_types.h | 1 +
mm/filemap.c | 2 ++
2 files changed, 3 insertions(+)

diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 79765e3dd8f3..6f0dbef7aa1f 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -1169,6 +1169,7 @@ enum fault_flag {
FAULT_FLAG_UNSHARE = 1 << 10,
FAULT_FLAG_ORIG_PTE_VALID = 1 << 11,
FAULT_FLAG_VMA_LOCK = 1 << 12,
+ FAULT_FLAG_LOCK_DROPPED = 1 << 13,
};

typedef unsigned int __bitwise zap_flags_t;
diff --git a/mm/filemap.c b/mm/filemap.c
index 87b335a93530..8ad06d69895b 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1723,6 +1723,7 @@ vm_fault_t __folio_lock_fault(struct folio *folio, struct vm_fault *vmf)
return VM_FAULT_RETRY;

mmap_read_unlock(mm);
+ vmf->flags |= FAULT_FLAG_LOCK_DROPPED;
if (vmf->flags & FAULT_FLAG_KILLABLE)
folio_wait_locked_killable(folio);
else
@@ -1735,6 +1736,7 @@ vm_fault_t __folio_lock_fault(struct folio *folio, struct vm_fault *vmf)
ret = __folio_lock_killable(folio);
if (ret) {
mmap_read_unlock(mm);
+ vmf->flags |= FAULT_FLAG_LOCK_DROPPED;
return VM_FAULT_RETRY;
}
} else {
--
2.41.0.178.g377b9f9a00-goog