[PATCH] Re: zero-filed page on VOP_PUTPAGES

[Emmanuel Dreyfus <manu%netbsd.org@localhost>]

On Fri, Aug 19, 2011 at 01:54:28PM +0000, Emmanuel Dreyfus wrote:
> Here is my complete anlysis of the problem:
(snip)

And here is a fix in puffs_vnop_getattr(). It was tested on netbsd-5 only so 
far since the bug does not appear in -current. My test case does not exhibit
the bug anymore on netbsd-5.

Opinions?

I obtain this without yamt's patch that flushes writes in dosetattr()
before sending the SETATTR message. I wonder if this is really a 
different problem. yamt, how do you get the problem that is fixed by
your patch? I would like to check if I can reproduce.

Index: sys/fs/puffs/puffs_vnops.c
===================================================================
RCS file: /cvsroot/src/sys/fs/puffs/puffs_vnops.c,v
retrieving revision 1.129.4.9
diff -U 4 -r1.129.4.9 puffs_vnops.c
--- sys/fs/puffs/puffs_vnops.c  17 Jul 2011 15:36:03 -0000      1.129.4.9
+++ sys/fs/puffs/puffs_vnops.c  19 Aug 2011 15:37:53 -0000
@@ -897,8 +897,21 @@
                vap->va_size = pn->pn_mc_size;
        } else {
                if (rvap->va_size != VNOVAL
                    && vp->v_type != VBLK && vp->v_type != VCHR) {
+                       /*
+                        * There may be a pending SETATTR triggered by
+                        * another process (e.g.: syncer). The kernel
+                        * is waiting in dosetattr() and decided on
+                        * a newer and bigger size. If we report a
+                        * smaller and older size from the filesystem,
+                        * uvm_vnp_setsize() will truncate the file and
+                        * discard the cached data not yet written. We
+                        * therefore retain the biggest value from 
+                        * kernel and filesystem to avoid data corruption.
+                        */
+                       rvap->va_size = MAX(rvap->va_size, vp->v_size);
+
                        uvm_vnp_setsize(vp, rvap->va_size);
                        pn->pn_serversize = rvap->va_size;
                }
        }


-- 
Emmanuel Dreyfus
manu%netbsd.org@localhost