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fix: acquire lru_lock before pinning frames to avoid race condition with eviction

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EDiasAlberto
2024-12-06 13:20:43 +00:00
parent 8ac34063d7
commit d389c15828
2 changed files with 11 additions and 5 deletions
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10
src/vm/frame.c
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@@ -28,9 +28,6 @@ struct list lru_list;
victim. Otherwise, the next element in the queue is similarly considered. */ victim. Otherwise, the next element in the queue is similarly considered. */
struct list_elem *next_victim = NULL; struct list_elem *next_victim = NULL;
/* Synchronisation variables. */
/* Protects access to 'lru_list'. */
struct lock lru_lock;
struct frame_metadata struct frame_metadata
{ {
@@ -175,23 +172,29 @@ frame_alloc (enum palloc_flags flags, void *upage, struct thread *owner)
void void
frame_pin (void *frame) frame_pin (void *frame)
{ {
ASSERT (frame != NULL);
lock_acquire (&lru_lock);
struct frame_metadata *frame_metadata = frame_metadata_get (frame); struct frame_metadata *frame_metadata = frame_metadata_get (frame);
if (frame_metadata == NULL) if (frame_metadata == NULL)
PANIC ("Attempted to pin a frame at an unallocated kernel address '%p'\n", PANIC ("Attempted to pin a frame at an unallocated kernel address '%p'\n",
frame); frame);
frame_metadata->pinned = true; frame_metadata->pinned = true;
lock_release (&lru_lock);
} }
void void
frame_unpin (void *frame) frame_unpin (void *frame)
{ {
ASSERT (frame != NULL);
lock_acquire (&lru_lock);
struct frame_metadata *frame_metadata = frame_metadata_get (frame); struct frame_metadata *frame_metadata = frame_metadata_get (frame);
if (frame_metadata == NULL) if (frame_metadata == NULL)
PANIC ("Attempted to unpin a frame at an unallocated kernel address '%p'\n", PANIC ("Attempted to unpin a frame at an unallocated kernel address '%p'\n",
frame); frame);
frame_metadata->pinned = false; frame_metadata->pinned = false;
lock_release (&lru_lock);
} }
/* Attempt to deallocate a frame for a user process by removing it from the /* Attempt to deallocate a frame for a user process by removing it from the
@@ -372,7 +375,6 @@ frame_metadata_get (void *frame)
struct hash_elem *e = hash_find (&frame_table, &key_metadata.hash_elem); struct hash_elem *e = hash_find (&frame_table, &key_metadata.hash_elem);
if (e == NULL) return NULL; if (e == NULL) return NULL;
return hash_entry (e, struct frame_metadata, hash_elem); return hash_entry (e, struct frame_metadata, hash_elem);
} }

4
src/vm/frame.h
View File

@@ -10,7 +10,11 @@ struct frame_owner
struct list_elem elem; /* List element for the list of owners. */ struct list_elem elem; /* List element for the list of owners. */
}; };
/* Synchronisation variables. */
/* Protects access to 'lru_list'. */
struct lock lru_lock;
void frame_init (void); void frame_init (void);
void *frame_alloc (enum palloc_flags, void *, struct thread *); void *frame_alloc (enum palloc_flags, void *, struct thread *);
void frame_pin (void *frame); void frame_pin (void *frame);
void frame_unpin (void *frame); void frame_unpin (void *frame);