diff options
Diffstat (limited to 'include/linux/mmap_lock.h')
| -rw-r--r-- | include/linux/mmap_lock.h | 41 |
1 files changed, 41 insertions, 0 deletions
diff --git a/include/linux/mmap_lock.h b/include/linux/mmap_lock.h index 5da384bd0a26..11a078de9150 100644 --- a/include/linux/mmap_lock.h +++ b/include/linux/mmap_lock.h @@ -12,6 +12,7 @@ extern int rcuwait_wake_up(struct rcuwait *w); #include <linux/tracepoint-defs.h> #include <linux/types.h> #include <linux/cleanup.h> +#include <linux/sched/mm.h> #define MMAP_LOCK_INITIALIZER(name) \ .mmap_lock = __RWSEM_INITIALIZER((name).mmap_lock), @@ -154,6 +155,10 @@ static inline void vma_refcount_put(struct vm_area_struct *vma) * reused and attached to a different mm before we lock it. * Returns the vma on success, NULL on failure to lock and EAGAIN if vma got * detached. + * + * WARNING! The vma passed to this function cannot be used if the function + * fails to lock it because in certain cases RCU lock is dropped and then + * reacquired. Once RCU lock is dropped the vma can be concurently freed. */ static inline struct vm_area_struct *vma_start_read(struct mm_struct *mm, struct vm_area_struct *vma) @@ -183,6 +188,31 @@ static inline struct vm_area_struct *vma_start_read(struct mm_struct *mm, } rwsem_acquire_read(&vma->vmlock_dep_map, 0, 1, _RET_IP_); + + /* + * If vma got attached to another mm from under us, that mm is not + * stable and can be freed in the narrow window after vma->vm_refcnt + * is dropped and before rcuwait_wake_up(mm) is called. Grab it before + * releasing vma->vm_refcnt. + */ + if (unlikely(vma->vm_mm != mm)) { + /* Use a copy of vm_mm in case vma is freed after we drop vm_refcnt */ + struct mm_struct *other_mm = vma->vm_mm; + + /* + * __mmdrop() is a heavy operation and we don't need RCU + * protection here. Release RCU lock during these operations. + * We reinstate the RCU read lock as the caller expects it to + * be held when this function returns even on error. + */ + rcu_read_unlock(); + mmgrab(other_mm); + vma_refcount_put(vma); + mmdrop(other_mm); + rcu_read_lock(); + return NULL; + } + /* * Overflow of vm_lock_seq/mm_lock_seq might produce false locked result. * False unlocked result is impossible because we modify and check @@ -309,6 +339,17 @@ void vma_mark_detached(struct vm_area_struct *vma); struct vm_area_struct *lock_vma_under_rcu(struct mm_struct *mm, unsigned long address); +/* + * Locks next vma pointed by the iterator. Confirms the locked vma has not + * been modified and will retry under mmap_lock protection if modification + * was detected. Should be called from read RCU section. + * Returns either a valid locked VMA, NULL if no more VMAs or -EINTR if the + * process was interrupted. + */ +struct vm_area_struct *lock_next_vma(struct mm_struct *mm, + struct vma_iterator *iter, + unsigned long address); + #else /* CONFIG_PER_VMA_LOCK */ static inline void mm_lock_seqcount_init(struct mm_struct *mm) {} |