Further refine the handling of stop signals in the NFS client. The

changes in r246417 were incomplete as they did not add explicit calls to
sigdeferstop() around all the places that previously passed SBDRY to
_sleep().  In addition, nfs_getcacheblk() could trigger a write RPC from
getblk() resulting in sigdeferstop() recursing.  Rather than manually
deferring stop signals in specific places, change the VFS_*() and VOP_*()
methods to defer stop signals for filesystems which request this behavior
via a new VFCF_SBDRY flag.  Note that this has to be a VFC flag rather than
a MNTK flag so that it works properly with VFS_MOUNT() when the mount is
not yet fully constructed.  For now, only the NFS clients are set this new
flag in VFS_SET().

A few other related changes:
- Add an assertion to ensure that TDF_SBDRY doesn't leak to userland.
- When a lookup request uses VOP_READLINK() to follow a symlink, mark
  the request as being on behalf of the thread performing the lookup
  (cnp_thread) rather than using a NULL thread pointer.  This causes
  NFS to properly handle signals during this VOP on an interruptible
  mount.

PR:		kern/176179
Reported by:	Russell Cattelan (sigdeferstop() recursion)
Reviewed by:	kib
MFC after:	1 month

11 files changed, 141 insertions, 41 deletions

diff --git a/sys/fs/nfs/nfs_commonkrpc.c b/sys/fs/nfs/nfs_commonkrpc.c
index f08ba85..86b6987 100644
--- a/sys/fs/nfs/nfs_commonkrpc.c
+++ b/sys/fs/nfs/nfs_commonkrpc.c
@@ -1080,7 +1080,6 @@ newnfs_set_sigmask(struct thread *td, sigset_t *oldset)
 			SIGDELSET(newset, newnfs_sig_set[i]);
 	}
 	mtx_unlock(&p->p_sigacts->ps_mtx);
-	sigdeferstop(td);
 	kern_sigprocmask(td, SIG_SETMASK, &newset, oldset,
 	    SIGPROCMASK_PROC_LOCKED);
 	PROC_UNLOCK(p);
@@ -1092,7 +1091,6 @@ newnfs_restore_sigmask(struct thread *td, sigset_t *set)
 	if (td == NULL)
 		td = curthread; /* XXX */
 	kern_sigprocmask(td, SIG_SETMASK, set, NULL, 0);
-	sigallowstop(td);
 }
 
 /*
diff --git a/sys/fs/nfsclient/nfs_clvfsops.c b/sys/fs/nfsclient/nfs_clvfsops.c
index 83ce3cb..281ce44 100644
--- a/sys/fs/nfsclient/nfs_clvfsops.c
+++ b/sys/fs/nfsclient/nfs_clvfsops.c
@@ -132,7 +132,7 @@ static struct vfsops nfs_vfsops = {
 	.vfs_unmount =		nfs_unmount,
 	.vfs_sysctl =		nfs_sysctl,
 };
-VFS_SET(nfs_vfsops, nfs, VFCF_NETWORK);
+VFS_SET(nfs_vfsops, nfs, VFCF_NETWORK | VFCF_SBDRY);
 
 /* So that loader and kldload(2) can find us, wherever we are.. */
 MODULE_VERSION(nfs, 1);
diff --git a/sys/kern/kern_sig.c b/sys/kern/kern_sig.c
index 7d3634d..e1dbedc 100644
--- a/sys/kern/kern_sig.c
+++ b/sys/kern/kern_sig.c
@@ -2537,16 +2537,22 @@ tdsigcleanup(struct thread *td)
 
 }
 
-/* Defer the delivery of SIGSTOP for the current thread. */
-void
-sigdeferstop(struct thread *td)
+/*
+ * Defer the delivery of SIGSTOP for the current thread.  Returns true
+ * if stops were deferred and false if they were already deferred.
+ */
+int
+sigdeferstop(void)
 {
+	struct thread *td;
 
-	KASSERT(!(td->td_flags & TDF_SBDRY),
-	    ("attempt to set TDF_SBDRY recursively"));
+	td = curthread;
+	if (td->td_flags & TDF_SBDRY)
+		return (0);
 	thread_lock(td);
 	td->td_flags |= TDF_SBDRY;
 	thread_unlock(td);
+	return (1);
 }
 
 /*
@@ -2555,11 +2561,11 @@ sigdeferstop(struct thread *td)
  * will suspend either via ast() or a subsequent interruptible sleep.
  */
 void
-sigallowstop(struct thread *td)
+sigallowstop()
 {
+	struct thread *td;
 
-	KASSERT(td->td_flags & TDF_SBDRY,
-	    ("attempt to clear already-cleared TDF_SBDRY"));
+	td = curthread;
 	thread_lock(td);
 	td->td_flags &= ~TDF_SBDRY;
 	thread_unlock(td);
diff --git a/sys/kern/subr_trap.c b/sys/kern/subr_trap.c
index 22cabcb..bd06f20 100644
--- a/sys/kern/subr_trap.c
+++ b/sys/kern/subr_trap.c
@@ -164,6 +164,8 @@ userret(struct thread *td, struct trapframe *frame)
 	    ("userret: Returning with with pinned thread"));
 	KASSERT(td->td_vp_reserv == 0,
 	    ("userret: Returning while holding vnode reservation"));
+	KASSERT((td->td_flags & TDF_SBDRY) == 0,
+	    ("userret: Returning with stop signals deferred"));
 #ifdef VIMAGE
 	/* Unfortunately td_vnet_lpush needs VNET_DEBUG. */
 	VNET_ASSERT(curvnet == NULL,
diff --git a/sys/kern/vfs_export.c b/sys/kern/vfs_export.c
index 114c23e..6a3f291 100644
--- a/sys/kern/vfs_export.c
+++ b/sys/kern/vfs_export.c
@@ -49,6 +49,7 @@ __FBSDID("$FreeBSD$");
 #include <sys/mutex.h>
 #include <sys/rwlock.h>
 #include <sys/refcount.h>
+#include <sys/signalvar.h>
 #include <sys/socket.h>
 #include <sys/systm.h>
 #include <sys/vnode.h>
diff --git a/sys/kern/vfs_lookup.c b/sys/kern/vfs_lookup.c
index e5ee4f6..fbde152 100644
--- a/sys/kern/vfs_lookup.c
+++ b/sys/kern/vfs_lookup.c
@@ -339,7 +339,7 @@ namei(struct nameidata *ndp)
 		auio.uio_offset = 0;
 		auio.uio_rw = UIO_READ;
 		auio.uio_segflg = UIO_SYSSPACE;
-		auio.uio_td = (struct thread *)0;
+		auio.uio_td = td;
 		auio.uio_resid = MAXPATHLEN;
 		error = VOP_READLINK(ndp->ni_vp, &auio, cnp->cn_cred);
 		if (error) {
diff --git a/sys/nfsclient/nfs_krpc.c b/sys/nfsclient/nfs_krpc.c
index 851b0b6..d3082d8 100644
--- a/sys/nfsclient/nfs_krpc.c
+++ b/sys/nfsclient/nfs_krpc.c
@@ -748,7 +748,6 @@ nfs_set_sigmask(struct thread *td, sigset_t *oldset)
 			SIGDELSET(newset, nfs_sig_set[i]);
 	}
 	mtx_unlock(&p->p_sigacts->ps_mtx);
-	sigdeferstop(td);
 	kern_sigprocmask(td, SIG_SETMASK, &newset, oldset,
 	    SIGPROCMASK_PROC_LOCKED);
 	PROC_UNLOCK(p);
@@ -760,7 +759,6 @@ nfs_restore_sigmask(struct thread *td, sigset_t *set)
 	if (td == NULL)
 		td = curthread; /* XXX */
 	kern_sigprocmask(td, SIG_SETMASK, set, NULL, 0);
-	sigallowstop(td);
 }
 
 /*
diff --git a/sys/nfsclient/nfs_vfsops.c b/sys/nfsclient/nfs_vfsops.c
index 63b5772..9cec307 100644
--- a/sys/nfsclient/nfs_vfsops.c
+++ b/sys/nfsclient/nfs_vfsops.c
@@ -146,7 +146,7 @@ static struct vfsops nfs_vfsops = {
 	.vfs_unmount =		nfs_unmount,
 	.vfs_sysctl =		nfs_sysctl,
 };
-VFS_SET(nfs_vfsops, oldnfs, VFCF_NETWORK);
+VFS_SET(nfs_vfsops, oldnfs, VFCF_NETWORK | VFCF_SBDRY);
 
 /* So that loader and kldload(2) can find us, wherever we are.. */
 MODULE_VERSION(oldnfs, 1);
diff --git a/sys/sys/mount.h b/sys/sys/mount.h
index bbbc569..f73d5d7 100644
--- a/sys/sys/mount.h
+++ b/sys/sys/mount.h
@@ -493,6 +493,7 @@ struct ovfsconf {
 #define	VFCF_UNICODE	0x00200000	/* stores file names as Unicode */
 #define	VFCF_JAIL	0x00400000	/* can be mounted from within a jail */
 #define	VFCF_DELEGADMIN	0x00800000	/* supports delegated administration */
+#define	VFCF_SBDRY	0x01000000	/* defer stop requests */
 
 typedef uint32_t fsctlop_t;
 
@@ -629,30 +630,121 @@ struct vfsops {
 
 vfs_statfs_t	__vfs_statfs;
 
-#define	VFS_MOUNT(MP)		(*(MP)->mnt_op->vfs_mount)(MP)
-#define	VFS_UNMOUNT(MP, FORCE)	(*(MP)->mnt_op->vfs_unmount)(MP, FORCE)
-#define	VFS_ROOT(MP, FLAGS, VPP)					\
-	(*(MP)->mnt_op->vfs_root)(MP, FLAGS, VPP)
-#define	VFS_QUOTACTL(MP, C, U, A)					\
-	(*(MP)->mnt_op->vfs_quotactl)(MP, C, U, A)
-#define	VFS_STATFS(MP, SBP)	__vfs_statfs((MP), (SBP))
-#define	VFS_SYNC(MP, WAIT)	(*(MP)->mnt_op->vfs_sync)(MP, WAIT)
-#define VFS_VGET(MP, INO, FLAGS, VPP) \
-	(*(MP)->mnt_op->vfs_vget)(MP, INO, FLAGS, VPP)
-#define VFS_FHTOVP(MP, FIDP, FLAGS, VPP) \
-	(*(MP)->mnt_op->vfs_fhtovp)(MP, FIDP, FLAGS, VPP)
-#define VFS_CHECKEXP(MP, NAM, EXFLG, CRED, NUMSEC, SEC)	\
-	(*(MP)->mnt_op->vfs_checkexp)(MP, NAM, EXFLG, CRED, NUMSEC, SEC)
-#define	VFS_EXTATTRCTL(MP, C, FN, NS, N)				\
-	(*(MP)->mnt_op->vfs_extattrctl)(MP, C, FN, NS, N)
-#define VFS_SYSCTL(MP, OP, REQ) \
-	(*(MP)->mnt_op->vfs_sysctl)(MP, OP, REQ)
-#define	VFS_SUSP_CLEAN(MP) \
-	({if (*(MP)->mnt_op->vfs_susp_clean != NULL)		\
-	       (*(MP)->mnt_op->vfs_susp_clean)(MP); })
-#define	VFS_RECLAIM_LOWERVP(MP, VP)				\
-	({if (*(MP)->mnt_op->vfs_reclaim_lowervp != NULL)	\
-		(*(MP)->mnt_op->vfs_reclaim_lowervp)((MP), (VP)); })
+#define	VFS_PROLOGUE(MP)	do {					\
+	int _enable_stops;						\
+									\
+	_enable_stops = ((MP) != NULL &&				\
+	    ((MP)->mnt_vfc->vfc_flags & VFCF_SBDRY) && sigdeferstop())
+
+#define	VFS_EPILOGUE(MP)						\
+	if (_enable_stops)						\
+		sigallowstop();						\
+} while (0)
+
+#define	VFS_MOUNT(MP) ({						\
+	int _rc;							\
+									\
+	VFS_PROLOGUE(MP);						\
+	_rc = (*(MP)->mnt_op->vfs_mount)(MP);				\
+	VFS_EPILOGUE(MP);						\
+	_rc; })
+
+#define	VFS_UNMOUNT(MP, FORCE) ({					\
+	int _rc;							\
+									\
+	VFS_PROLOGUE(MP);						\
+	_rc = (*(MP)->mnt_op->vfs_unmount)(MP, FORCE);			\
+	VFS_EPILOGUE(MP);						\
+	_rc; })
+
+#define	VFS_ROOT(MP, FLAGS, VPP) ({					\
+	int _rc;							\
+									\
+	VFS_PROLOGUE(MP);						\
+	_rc = (*(MP)->mnt_op->vfs_root)(MP, FLAGS, VPP);		\
+	VFS_EPILOGUE(MP);						\
+	_rc; })
+
+#define	VFS_QUOTACTL(MP, C, U, A) ({					\
+	int _rc;							\
+									\
+	VFS_PROLOGUE(MP);						\
+	_rc = (*(MP)->mnt_op->vfs_quotactl)(MP, C, U, A);		\
+	VFS_EPILOGUE(MP);						\
+	_rc; })
+
+#define	VFS_STATFS(MP, SBP) ({						\
+	int _rc;							\
+									\
+	VFS_PROLOGUE(MP);						\
+	_rc = __vfs_statfs((MP), (SBP));				\
+	VFS_EPILOGUE(MP);						\
+	_rc; })
+
+#define	VFS_SYNC(MP, WAIT) ({						\
+	int _rc;							\
+									\
+	VFS_PROLOGUE(MP);						\
+	_rc = (*(MP)->mnt_op->vfs_sync)(MP, WAIT);			\
+	VFS_EPILOGUE(MP);						\
+	_rc; })
+
+#define	VFS_VGET(MP, INO, FLAGS, VPP) ({				\
+	int _rc;							\
+									\
+	VFS_PROLOGUE(MP);						\
+	_rc = (*(MP)->mnt_op->vfs_vget)(MP, INO, FLAGS, VPP);		\
+	VFS_EPILOGUE(MP);						\
+	_rc; })
+
+#define	VFS_FHTOVP(MP, FIDP, FLAGS, VPP) ({				\
+	int _rc;							\
+									\
+	VFS_PROLOGUE(MP);						\
+	_rc = (*(MP)->mnt_op->vfs_fhtovp)(MP, FIDP, FLAGS, VPP);	\
+	VFS_EPILOGUE(MP);						\
+	_rc; })
+
+#define	VFS_CHECKEXP(MP, NAM, EXFLG, CRED, NUMSEC, SEC) ({		\
+	int _rc;							\
+									\
+	VFS_PROLOGUE(MP);						\
+	_rc = (*(MP)->mnt_op->vfs_checkexp)(MP, NAM, EXFLG, CRED, NUMSEC,\
+	    SEC);							\
+	VFS_EPILOGUE(MP);						\
+	_rc; })
+
+#define	VFS_EXTATTRCTL(MP, C, FN, NS, N) ({				\
+	int _rc;							\
+									\
+	VFS_PROLOGUE(MP);						\
+	_rc = (*(MP)->mnt_op->vfs_extattrctl)(MP, C, FN, NS, N);	\
+	VFS_EPILOGUE(MP);						\
+	_rc; })
+
+#define	VFS_SYSCTL(MP, OP, REQ) ({					\
+	int _rc;							\
+									\
+	VFS_PROLOGUE(MP);						\
+	_rc = (*(MP)->mnt_op->vfs_sysctl)(MP, OP, REQ);			\
+	VFS_EPILOGUE(MP);						\
+	_rc; })
+
+#define	VFS_SUSP_CLEAN(MP) do {						\
+	if (*(MP)->mnt_op->vfs_susp_clean != NULL) {			\
+		VFS_PROLOGUE(MP);					\
+		(*(MP)->mnt_op->vfs_susp_clean)(MP);			\
+		VFS_EPILOGUE(MP);					\
+	}								\
+} while (0)
+
+#define	VFS_RECLAIM_LOWERVP(MP, VP) do {				\
+	if (*(MP)->mnt_op->vfs_reclaim_lowervp != NULL) {		\
+		VFS_PROLOGUE(MP);					\
+		(*(MP)->mnt_op->vfs_reclaim_lowervp)((MP), (VP));	\
+		VFS_EPILOGUE(MP);					\
+	}								\
+} while (0)
 
 #define VFS_KNOTE_LOCKED(vp, hint) do					\
 {									\
diff --git a/sys/sys/signalvar.h b/sys/sys/signalvar.h
index 91655b2..fcf25ad 100644
--- a/sys/sys/signalvar.h
+++ b/sys/sys/signalvar.h
@@ -328,8 +328,8 @@ extern struct mtx	sigio_lock;
 #define	SIGPROCMASK_PS_LOCKED	0x0004
 
 int	cursig(struct thread *td, int stop_allowed);
-void	sigdeferstop(struct thread *td);
-void	sigallowstop(struct thread *td);
+int	sigdeferstop(void);
+void	sigallowstop(void);
 void	execsigs(struct proc *p);
 void	gsignal(int pgid, int sig, ksiginfo_t *ksi);
 void	killproc(struct proc *p, char *why);
diff --git a/sys/tools/vnode_if.awk b/sys/tools/vnode_if.awk
index c991458..2347004 100644
--- a/sys/tools/vnode_if.awk
+++ b/sys/tools/vnode_if.awk
@@ -172,6 +172,7 @@ if (cfile) {
 	    "#include <sys/kernel.h>\n" \
 	    "#include <sys/mount.h>\n" \
 	    "#include <sys/sdt.h>\n" \
+	    "#include <sys/signalvar.h>\n" \
 	    "#include <sys/systm.h>\n" \
 	    "#include <sys/vnode.h>\n" \
 	    "\n" \
@@ -365,10 +366,12 @@ while ((getline < srcfile) > 0) {
 			add_debug_code(name, args[i], "Entry", "\t");
 		printc("\tKTR_START" ctrstr);
 		add_pre(name);
+		printc("\tVFS_PROLOGUE(a->a_" args[0]"->v_mount);")
 		printc("\tif (vop->"name" != NULL)")
 		printc("\t\trc = vop->"name"(a);")
 		printc("\telse")
 		printc("\t\trc = vop->vop_bypass(&a->a_gen);")
+		printc("\tVFS_EPILOGUE(a->a_" args[0]"->v_mount);")
 		printc("\tSDT_PROBE(vfs, vop, " name ", return, a->a_" args[0] ", a, rc, 0, 0);\n");
 		printc("\tif (rc == 0) {");
 		for (i = 0; i < numargs; ++i)