Re: PUFFS and existing file that get ENOENT

[manu%netbsd.org@localhost (Emmanuel Dreyfus)]

YAMAMOTO Takashi <yamt%mwd.biglobe.ne.jp@localhost> wrote:

> > Further investigation shows that this ENOENT is returned by vget() call
> > in puffs_cookie2vnode(). That suggests some kind of race condition, but
> > that is not obvious. It means a vnode has been created on a lookup, then
> > it gets recycled while looking up one of its child.
> it should retry from puffs_cookie2pnode in that case.

I first tried to loop on vget but got a panic because I did not hold
v_interlock anymore. I then came to this patch and got a uvm_fault (backtrace
below)

Index: sys/fs/puffs/puffs_node.c
===================================================================
RCS file: /cvsroot/src/sys/fs/puffs/puffs_node.c,v
retrieving revision 1.13.10.3
diff -U 4 -r1.13.10.3 puffs_node.c
--- sys/fs/puffs/puffs_node.c   2 Nov 2011 20:11:12 -0000       1.13.10.3
+++ sys/fs/puffs/puffs_node.c   17 Jan 2012 02:36:02 -0000
@@ -56,8 +56,9 @@
        .gop_alloc, should ask userspace
 #endif
 };
 
+static __inline int puffs_vget(struct puffs_mount *, struct vnode *, int);
 static __inline struct puffs_node_hashlist
        *puffs_cookie2hashlist(struct puffs_mount *, puffs_cookie_t);
 static struct puffs_node *puffs_cookie2pnode(struct puffs_mount *,
                                             puffs_cookie_t);
@@ -271,8 +272,23 @@
 
        return;
 }
 
+static __inline int puffs_vget(struct puffs_mount *pmp,
+       struct vnode *vp, int flags)
+{
+       int rv;
+
+       while ((rv = vget(vp, flags)) == ENOENT) {
+               printf("*** retry vget %p\n", vp); 
+               mutex_enter(&pmp->pmp_lock);
+               mutex_enter(&vp->v_interlock);
+               mutex_exit(&pmp->pmp_lock);
+       }
+
+       return rv;
+}
+
 static __inline struct puffs_node_hashlist *
 puffs_cookie2hashlist(struct puffs_mount *pmp, puffs_cookie_t ck)
 {
        uint32_t hash;
@@ -320,9 +336,9 @@
        vp = pmp->pmp_root;
        if (vp) {
                mutex_enter(&vp->v_interlock);
                mutex_exit(&pmp->pmp_lock);
-               if (vget(vp, LK_INTERLOCK) == 0)
+               if (puffs_vget(pmp, vp, LK_INTERLOCK) == 0)
                        return 0;
        } else
                mutex_exit(&pmp->pmp_lock);
 
@@ -405,9 +421,9 @@
 
        vgetflags = LK_INTERLOCK;
        if (lock)
                vgetflags |= LK_EXCLUSIVE | LK_RETRY;
-       if ((rv = vget(vp, vgetflags)))
+       if ((rv = puffs_vget(pmp, vp, vgetflags)))
                return rv;
 
        *vpp = vp;
        return 0;



It produced a uvm_fault in the domU, followed by a crash of the dom0 (no
console access on that one, I do not have the dom0 backtrace yet). Here is
what I have been able to copy/paste from the domU (only the panic string is
missing):

trap type 6 code 0 eip c03012da cs 9 eflags 10283 cr2 0 ilevel 7
kernel: supervisor trap page fault, code=0
Stopped in pid 18692.1 (sh) at  netbsd:turnstile_block+0x1aa:   movl
0x10(%eax),%eax
db> bt
turnstile_block(0,1,cb5b42ec,c046d89c,cc3baa9c,cb91ba60,0,cb5b42ec,1,cb4c3000)
at netbsd:turnstile_block+0x1aa
mutex_vector_enter(cb5b42ec,cb5b42ec,0,0,cb3fc39c,cb497000,cc3baacc,c0365ff8,c
c3baac0,6) at netbsd:mutex_vector_enter+0xfa
puffs_cookie2vnode(cb4c3000,bb9090c0,1,1,cc3bab38,0,cc3bab4c,c0350467,cb497000
,cc3bab38) at netbsd:puffs_cookie2vnode+0x187
puffs_vfsop_root(cb497000,cc3bab38,cc3bac28,20002,ca21dc38,ca215bdc,cc3bab2c,c
0365fc5,20,0) at netbsd:puffs_vfsop_root+0x38
lookup(cc3bac00,20002,400,cc3bac1c,cb31a0b8,cb31a0e0,cc3babac,c0355e6c,cc3bac1
c,cc3bab9f) at netbsd:lookup+0x287
namei(cc3bac00,cc3bac70,cc3bac0c,c03bc307,1964000,0,cc3bac3c,bb9067cc,0,0) at
netbsd:namei+0x144
do_sys_stat(bb9067cc,0,cc3bac70,c02e40b0,c0470dc8,0,3bac8c,cb01,41ed,369ddb94)
at netbsd:do_sys_stat+0x37
sys___lstat30(cb91ba60,cc3bad00,cc3bad28,bb916010,c03bc307,61cb000,0,bb9067cc,
bfbfde68,bfbfded8) at netbsd:sys___lstat30+0x29
syscall(cc3bad48,1f,1f,1f,1f,805fced,bb906797,bfbfded8,bb906796,bb9067dc) at
netbsd:syscall+0xc7


-- 
Emmanuel Dreyfus
http://hcpnet.free.fr/pubz
manu%netbsd.org@localhost