Re: wapbl + discard panic

[Taylor R Campbell]

   Date: Mon, 10 Aug 2015 21:31:07 -0700
   From: Jeff Rizzo <r...@tastylime.net>

   I'm guessing at the moment the answer is "don't do that," but it looks 
   like wapbl and discard aren't playing nice together:

   panic: kernel diagnostic assertion "rw_lock_held(&wl->wl_rwlock)" 

Try attached patch?

Index: sys/ufs/ffs/ffs_alloc.c
===================================================================
RCS file: /cvsroot/src/sys/ufs/ffs/ffs_alloc.c,v
retrieving revision 1.149
diff -p -u -r1.149 ffs_alloc.c
--- sys/ufs/ffs/ffs_alloc.c     28 Mar 2015 19:24:04 -0000      1.149
+++ sys/ufs/ffs/ffs_alloc.c     11 Aug 2015 04:55:37 -0000
@@ -1553,12 +1553,21 @@ struct discarddata {
 static void
 ffs_blkfree_td(struct fs *fs, struct discardopdata *td)
 {
+       struct mount *mp = spec_node_getmountedfs(td->devvp);
        long todo;
+       int error;
 
        while (td->size) {
                todo = min(td->size,
                  ffs_lfragtosize(fs, (fs->fs_frag - ffs_fragnum(fs, 
td->bno))));
+               error = UFS_WAPBL_BEGIN(mp);
+               if (error) {
+                       printf("ffs: failed to begin wapbl transaction"
+                           " for discard: %d\n", error);
+                       break;
+               }
                ffs_blkfree_cg(fs, td->devvp, td->bno, todo);
+               UFS_WAPBL_END(mp);
                td->bno += ffs_numfrags(fs, todo);
                td->size -= todo;
        }