On 07/02/2014 09:09 PM, Hugh Dickins wrote:
This reverts commit f00cdc6df7d7cfcabb5b740911e6788cb0802bdb.
(a) It was buggy: Sasha sent a lockdep report to remind us that grabbing
i_mutex in the fault path is a no-no (write syscall may already hold
i_mutex while faulting user buffer), no matter that the patch took care
to drop mmap_sem first.
(b) It may be thought too elaborate: see the diffstat.
(c) Vlastimil proposed a preferred approach, better for backporting to
v3.1..v3.4, which had madvise hole-punch support before the fallocate
infrastructure used in that commit - backporting being required once
the issue fixed was tagged with CVE-2014-4171.
(d) Hugh noticed a further pessimization fix needed in the same area.
Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Sasha Levin <sasha.levin@xxxxxxxxxx>
Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Konstantin Khlebnikov <koct9i@xxxxxxxxx>
Cc: Lukas Czerner <lczerner@xxxxxxxxxx>
Cc: Dave Jones <davej@xxxxxxxxxx>
---
mm/shmem.c | 56 +++------------------------------------------------
1 file changed, 4 insertions(+), 52 deletions(-)
--- 3.16-rc3/mm/shmem.c 2014-06-29 15:22:10.592003936 -0700
+++ linux/mm/shmem.c 2014-07-02 03:31:12.956546569 -0700
@@ -80,12 +80,11 @@ static struct vfsmount *shm_mnt;
#define SHORT_SYMLINK_LEN 128
/*
- * shmem_fallocate communicates with shmem_fault or shmem_writepage via
- * inode->i_private (with i_mutex making sure that it has only one user at
- * a time): we would prefer not to enlarge the shmem inode just for that.
+ * shmem_fallocate and shmem_writepage communicate via inode->i_private
+ * (with i_mutex making sure that it has only one user at a time):
+ * we would prefer not to enlarge the shmem inode just for that.
*/
struct shmem_falloc {
- int mode; /* FALLOC_FL mode currently operating */
pgoff_t start; /* start of range currently being fallocated */
pgoff_t next; /* the next page offset to be fallocated */
pgoff_t nr_falloced; /* how many new pages have been fallocated */
@@ -760,7 +759,6 @@ static int shmem_writepage(struct page *
spin_lock(&inode->i_lock);
shmem_falloc = inode->i_private;
if (shmem_falloc &&
- !shmem_falloc->mode &&
index >= shmem_falloc->start &&
index < shmem_falloc->next)
shmem_falloc->nr_unswapped++;
@@ -1235,44 +1233,6 @@ static int shmem_fault(struct vm_area_st
int error;
int ret = VM_FAULT_LOCKED;
- /*
- * 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.
- */
- if (unlikely(inode->i_private)) {
- struct shmem_falloc *shmem_falloc;
-
- spin_lock(&inode->i_lock);
- shmem_falloc = inode->i_private;
- if (!shmem_falloc ||
- shmem_falloc->mode != FALLOC_FL_PUNCH_HOLE ||
- 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 shmem_fallocate() 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 ((vmf->flags & FAULT_FLAG_ALLOW_RETRY) &&
- !(vmf->flags & FAULT_FLAG_RETRY_NOWAIT)) {
- up_read(&vma->vm_mm->mmap_sem);
- mutex_lock(&inode->i_mutex);
- mutex_unlock(&inode->i_mutex);
- return VM_FAULT_RETRY;
- }
- /* cond_resched? Leave that to GUP or return to user */
- return VM_FAULT_NOPAGE;
- }
- }
-
error = shmem_getpage(inode, vmf->pgoff, &vmf->page, SGP_CACHE, &ret);
if (error)
return ((error == -ENOMEM) ? VM_FAULT_OOM : VM_FAULT_SIGBUS);
@@ -1769,26 +1729,18 @@ static long shmem_fallocate(struct file
mutex_lock(&inode->i_mutex);
- shmem_falloc.mode = mode & ~FALLOC_FL_KEEP_SIZE;
-
if (mode & FALLOC_FL_PUNCH_HOLE) {
struct address_space *mapping = file->f_mapping;
loff_t unmap_start = round_up(offset, PAGE_SIZE);
loff_t unmap_end = round_down(offset + len, PAGE_SIZE) - 1;
- shmem_falloc.start = unmap_start >> PAGE_SHIFT;
- shmem_falloc.next = (unmap_end + 1) >> PAGE_SHIFT;
- spin_lock(&inode->i_lock);
- inode->i_private = &shmem_falloc;
- spin_unlock(&inode->i_lock);
-
if ((u64)unmap_end > (u64)unmap_start)
unmap_mapping_range(mapping, unmap_start,
1 + unmap_end - unmap_start, 0);
shmem_truncate_range(inode, offset, offset + len - 1);
/* No need to unmap again: hole-punching leaves COWed pages */
error = 0;
- goto undone;
+ goto out;
}
/* We need to check rlimit even when FALLOC_FL_KEEP_SIZE */
--
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