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

2 files changed, 1 insertions, 3 deletions

diff --git a/sys/nfsclient/nfs_krpc.c b/sys/nfsclient/nfs_krpc.c
index 851b0b618389..d3082d8d914f 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 63b5772f35ed..9cec3077fbcb 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);