Fix stack overflow in vn_rdwr() due to memory reclaim

Unless __GFP_IO and __GFP_FS are removed from the file mapping gfp
mask we may enter memory reclaim during IO.  In this case shrink_slab()
entered another file system which is notoriously hungry for stack.
This additional stack usage may cause a stack overflow.  This patch
removes __GFP_IO and __GFP_FS from the mapping gfp mask of each file
during vn_open() to avoid any reclaim in the vn_rdwr() IO path.  The
original mask is then restored at vn_close() time.  Hats off to the
loop driver which does something similiar for the same reason.

  [...]
  shrink_slab+0xdc/0x153
  try_to_free_pages+0x1da/0x2d7
  __alloc_pages+0x1d7/0x2da
  do_generic_mapping_read+0x2c9/0x36f
  file_read_actor+0x0/0x145
  __generic_file_aio_read+0x14f/0x19b
  generic_file_aio_read+0x34/0x39
  do_sync_read+0xc7/0x104
  vfs_read+0xcb/0x171
  :spl:vn_rdwr+0x2b8/0x402
  :zfs:vdev_file_io_start+0xad/0xe1
  [...]

Signed-off-by: Brian Behlendorf <[email protected]>

1 files changed, 6 insertions, 0 deletions

diff --git a/module/spl/spl-vnode.c b/module/spl/spl-vnode.c
index dd759bf7f..29028c3c0 100644
--- a/module/spl/spl-vnode.c
+++ b/module/spl/spl-vnode.c
@@ -104,6 +104,7 @@ vn_open(const char *path, uio_seg_t seg, int flags, int mode,
 	struct file *fp;
 	struct kstat stat;
 	int rc, saved_umask = 0;
+	gfp_t saved_gfp;
 	vnode_t *vp;
 	SENTRY;
 
@@ -145,9 +146,13 @@ vn_open(const char *path, uio_seg_t seg, int flags, int mode,
 		SRETURN(ENOMEM);
 	}
 
+	saved_gfp = mapping_gfp_mask(fp->f_mapping);
+	mapping_set_gfp_mask(fp->f_mapping, saved_gfp & ~(__GFP_IO|__GFP_FS));
+
 	mutex_enter(&vp->v_lock);
 	vp->v_type = vn_get_sol_type(stat.mode);
 	vp->v_file = fp;
+	vp->v_gfp_mask = saved_gfp;
 	*vpp = vp;
 	mutex_exit(&vp->v_lock);
 
@@ -237,6 +242,7 @@ vn_close(vnode_t *vp, int flags, int x1, int x2, void *x3, void *x4)
 	ASSERT(vp);
 	ASSERT(vp->v_file);
 
+	mapping_set_gfp_mask(vp->v_file->f_mapping, vp->v_gfp_mask);
 	rc = filp_close(vp->v_file, 0);
 	vn_free(vp);