[src/trunk]: src/sys/miscfs/genfs Genfs_getpages(): Break a deadlock where on...

[hannken <hannken%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/a0ef78056233
branches:  trunk
changeset: 758583:a0ef78056233
user:      hannken <hannken%NetBSD.org@localhost>
date:      Tue Nov 09 16:31:48 2010 +0000

description:
Genfs_getpages(): Break a deadlock where one thread runs VOP_GETPAGES(),
has busy pages and wants the wapbl lock as reader from wapbl_begin(),
another thread has the wapbl lock as reader and waits for a page from
the first thread.  Now a third thread calls wapbl_flush() and wants the
wapbl lock as writer.

Move the wapbl_begin() up to a point where genfs_getpages() has no busy
pages yet.

diffstat:

 sys/miscfs/genfs/genfs_io.c |  45 +++++++++++++++++++++++----------------------
 1 files changed, 23 insertions(+), 22 deletions(-)

diffs (92 lines):

diff -r 31802444a92d -r a0ef78056233 sys/miscfs/genfs/genfs_io.c
--- a/sys/miscfs/genfs/genfs_io.c       Tue Nov 09 16:30:26 2010 +0000
+++ b/sys/miscfs/genfs/genfs_io.c       Tue Nov 09 16:31:48 2010 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: genfs_io.c,v 1.41 2010/11/03 04:32:50 uebayasi Exp $   */
+/*     $NetBSD: genfs_io.c,v 1.42 2010/11/09 16:31:48 hannken Exp $    */
 
 /*
  * Copyright (c) 1982, 1986, 1989, 1993
@@ -31,7 +31,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: genfs_io.c,v 1.41 2010/11/03 04:32:50 uebayasi Exp $");
+__KERNEL_RCSID(0, "$NetBSD: genfs_io.c,v 1.42 2010/11/09 16:31:48 hannken Exp $");
 
 #include <sys/param.h>
 #include <sys/systm.h>
@@ -129,10 +129,11 @@
        kauth_cred_t const cred = curlwp->l_cred;               /* XXXUBC curlwp */
        const bool async = (flags & PGO_SYNCIO) == 0;
        const bool memwrite = (ap->a_access_type & VM_PROT_WRITE) != 0;
-       bool has_trans = false;
        const bool overwrite = (flags & PGO_OVERWRITE) != 0;
        const bool blockalloc = memwrite && (flags & PGO_NOBLOCKALLOC) == 0;
        const bool glocked = (flags & PGO_GLOCKHELD) != 0;
+       const bool need_wapbl = blockalloc && vp->v_mount->mnt_wapbl;
+       bool has_trans_wapbl = false;
        UVMHIST_FUNC("genfs_getpages"); UVMHIST_CALLED(ubchist);
 
        UVMHIST_LOG(ubchist, "vp %p off 0x%x/%x count %d",
@@ -294,9 +295,20 @@
        UVMHIST_LOG(ubchist, "ridx %d npages %d startoff %ld endoff %ld",
            ridx, npages, startoffset, endoffset);
 
-       if (!has_trans) {
+       if (!has_trans_wapbl) {
                fstrans_start(vp->v_mount, FSTRANS_SHARED);
-               has_trans = true;
+               /*
+                * XXX: This assumes that we come here only via
+                * the mmio path
+                */
+               if (need_wapbl) {
+                       error = WAPBL_BEGIN(vp->v_mount);
+                       if (error) {
+                               fstrans_done(vp->v_mount);
+                               goto out_err_free;
+                       }
+               }
+               has_trans_wapbl = true;
        }
 
        /*
@@ -621,22 +633,8 @@
         */
 
        if (!error && sawhole && blockalloc) {
-               /*
-                * XXX: This assumes that we come here only via
-                * the mmio path
-                */
-               if (vp->v_mount->mnt_wapbl) {
-                       error = WAPBL_BEGIN(vp->v_mount);
-               }
-
-               if (!error) {
-                       error = GOP_ALLOC(vp, startoffset,
-                           npages << PAGE_SHIFT, 0, cred);
-                       if (vp->v_mount->mnt_wapbl) {
-                               WAPBL_END(vp->v_mount);
-                       }
-               }
-
+               error = GOP_ALLOC(vp, startoffset,
+                   npages << PAGE_SHIFT, 0, cred);
                UVMHIST_LOG(ubchist, "gop_alloc off 0x%x/0x%x -> %d",
                    startoffset, npages << PAGE_SHIFT, error,0);
                if (!error) {
@@ -738,8 +736,11 @@
        if (pgs != NULL && pgs != pgs_onstack)
                kmem_free(pgs, pgs_size);
 out_err:
-       if (has_trans)
+       if (has_trans_wapbl) {
+               if (need_wapbl)
+                       WAPBL_END(vp->v_mount);
                fstrans_done(vp->v_mount);
+       }
        return error;
 }