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-rw-r--r--mm/shmem.c64
1 files changed, 44 insertions, 20 deletions
diff --git a/mm/shmem.c b/mm/shmem.c
index 042b4afbd684..ec7244bb03fc 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -82,6 +82,7 @@ static struct vfsmount *shm_mnt;
* a time): we would prefer not to enlarge the shmem inode just for that.
*/
struct shmem_falloc {
+ wait_queue_head_t *waitq; /* faults into hole wait for punch to end */
pgoff_t start; /* start of range currently being fallocated */
pgoff_t next; /* the next page offset to be fallocated */
};
@@ -1074,37 +1075,57 @@ static int shmem_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
* Trinity finds that probing a hole which tmpfs is punching can
* prevent the hole-punch from ever completing: which in turn
* locks writers out with its hold on i_mutex. So refrain from
- * faulting pages into the hole while it's being punched, and
- * wait on i_mutex to be released if vmf->flags permits.
+ * faulting pages into the hole while it's being punched. Although
+ * shmem_truncate_range() does remove the additions, it may be unable to
+ * keep up, as each new page needs its own unmap_mapping_range() call,
+ * and the i_mmap tree grows ever slower to scan if new vmas are added.
+ *
+ * It does not matter if we sometimes reach this check just before the
+ * hole-punch begins, so that one fault then races with the punch:
+ * we just need to make racing faults a rare case.
+ *
+ * The implementation below would be much simpler if we just used a
+ * standard mutex or completion: but we cannot take i_mutex in fault,
+ * and bloating every shmem inode for this unlikely case would be sad.
*/
if (unlikely(inode->i_private)) {
struct shmem_falloc *shmem_falloc;
spin_lock(&inode->i_lock);
shmem_falloc = inode->i_private;
- if (!shmem_falloc ||
- vmf->pgoff < shmem_falloc->start ||
- vmf->pgoff >= shmem_falloc->next)
- shmem_falloc = NULL;
- spin_unlock(&inode->i_lock);
- /*
- * i_lock has protected us from taking shmem_falloc seriously
- * once return from vmtruncate_range() went back up that stack.
- * i_lock does not serialize with i_mutex at all, but it does
- * not matter if sometimes we wait unnecessarily, or sometimes
- * miss out on waiting: we just need to make those cases rare.
- */
- if (shmem_falloc) {
+ if (shmem_falloc &&
+ vmf->pgoff >= shmem_falloc->start &&
+ vmf->pgoff < shmem_falloc->next) {
+ wait_queue_head_t *shmem_falloc_waitq;
+ DEFINE_WAIT(shmem_fault_wait);
+
+ ret = VM_FAULT_NOPAGE;
if ((vmf->flags & FAULT_FLAG_ALLOW_RETRY) &&
!(vmf->flags & FAULT_FLAG_RETRY_NOWAIT)) {
+ /* It's polite to up mmap_sem if we can */
up_read(&vma->vm_mm->mmap_sem);
- mutex_lock(&inode->i_mutex);
- mutex_unlock(&inode->i_mutex);
- return VM_FAULT_RETRY;
+ ret = VM_FAULT_RETRY;
}
- /* cond_resched? Leave that to GUP or return to user */
- return VM_FAULT_NOPAGE;
+
+ shmem_falloc_waitq = shmem_falloc->waitq;
+ prepare_to_wait(shmem_falloc_waitq, &shmem_fault_wait,
+ TASK_UNINTERRUPTIBLE);
+ spin_unlock(&inode->i_lock);
+ schedule();
+
+ /*
+ * shmem_falloc_waitq points into the vmtruncate_range()
+ * stack of the hole-punching task: shmem_falloc_waitq
+ * is usually invalid by the time we reach here, but
+ * finish_wait() does not dereference it in that case;
+ * though i_lock needed lest racing with wake_up_all().
+ */
+ spin_lock(&inode->i_lock);
+ finish_wait(shmem_falloc_waitq, &shmem_fault_wait);
+ spin_unlock(&inode->i_lock);
+ return ret;
}
+ spin_unlock(&inode->i_lock);
}
error = shmem_getpage(inode, vmf->pgoff, &vmf->page, SGP_CACHE, &ret);
@@ -1135,7 +1156,9 @@ int vmtruncate_range(struct inode *inode, loff_t lstart, loff_t lend)
struct address_space *mapping = inode->i_mapping;
loff_t unmap_start = round_up(lstart, PAGE_SIZE);
loff_t unmap_end = round_down(1 + lend, PAGE_SIZE) - 1;
+ DECLARE_WAIT_QUEUE_HEAD_ONSTACK(shmem_falloc_waitq);
+ shmem_falloc.waitq = &shmem_falloc_waitq;
shmem_falloc.start = unmap_start >> PAGE_SHIFT;
shmem_falloc.next = (unmap_end + 1) >> PAGE_SHIFT;
spin_lock(&inode->i_lock);
@@ -1150,6 +1173,7 @@ int vmtruncate_range(struct inode *inode, loff_t lstart, loff_t lend)
spin_lock(&inode->i_lock);
inode->i_private = NULL;
+ wake_up_all(&shmem_falloc_waitq);
spin_unlock(&inode->i_lock);
}
mutex_unlock(&inode->i_mutex);