> Date: Fri, 15 Oct 2021 14:04:08 +0300
> From: Vitaliy Makkoveev <[email protected]>
>
> The next diff before introduce rwlock(9) for UNIX sockets garbage
> collector data.
>
> Release `unp_lock' before call unp_internalize() and take it within when
> access garbage collector data such as `unp_rights', `unp_msgcount' and
> `unp_file'. The garbage collector rwlock(9) will be introduced with the
> following diff, but right now M_WAITOK/M_WAIT allocations moved outside
> rwlock(9) held.
>
> The lock order between fdplock() and `unp_lock' has changed to fdplock()
> -> `unp_lock'. unp_internalize() is the only place where these locks
> simultaneously held together so this order doesn't matter. This shoud be
> helpful to mpi@'s knote(9) work.
>
> sosend() releases solock() before m_getuio() call, so this socket could
> be disconnected before uipc_usrreq() called. uipc_usrreq() checks
> connection oriented sockets state or tries to connect datagram sockets
> after successful unp_internalize() call, so this introduced solock()
> release doesn't modify existing behavior.
Is it safe to call fptounp() without holding the lock?
> Index: sys/kern/uipc_usrreq.c
> ===================================================================
> RCS file: /cvs/src/sys/kern/uipc_usrreq.c,v
> retrieving revision 1.149
> diff -u -p -r1.149 uipc_usrreq.c
> --- sys/kern/uipc_usrreq.c 14 Oct 2021 23:05:10 -0000 1.149
> +++ sys/kern/uipc_usrreq.c 15 Oct 2021 11:03:16 -0000
> @@ -219,8 +219,13 @@ uipc_usrreq(struct socket *so, int req,
> break;
>
> case PRU_SEND:
> - if (control && (error = unp_internalize(control, p)))
> - break;
> + if (control) {
> + sounlock(so, SL_LOCKED);
> + error = unp_internalize(control, p);
> + solock(so);
> + if (error)
> + break;
> + }
> switch (so->so_type) {
>
> case SOCK_DGRAM: {
> @@ -973,8 +978,6 @@ unp_internalize(struct mbuf *control, st
> int i, error;
> int nfds, *ip, fd, neededspace;
>
> - rw_assert_wrlock(&unp_lock);
> -
> /*
> * Check for two potential msg_controllen values because
> * IETF stuck their nose in a place it does not belong.
> @@ -987,8 +990,13 @@ unp_internalize(struct mbuf *control, st
> return (EINVAL);
> nfds = (cm->cmsg_len - CMSG_ALIGN(sizeof(*cm))) / sizeof (int);
>
> - if (unp_rights + nfds > maxfiles / 10)
> + rw_enter_write(&unp_lock);
> + if (unp_rights + nfds > maxfiles / 10) {
> + rw_exit_write(&unp_lock);
> return (EMFILE);
> + }
> + unp_rights += nfds;
> + rw_exit_write(&unp_lock);
>
> /* Make sure we have room for the struct file pointers */
> morespace:
> @@ -997,8 +1005,10 @@ morespace:
> if (neededspace > m_trailingspace(control)) {
> char *tmp;
> /* if we already have a cluster, the message is just too big */
> - if (control->m_flags & M_EXT)
> - return (E2BIG);
> + if (control->m_flags & M_EXT) {
> + error = E2BIG;
> + goto nospace;
> + }
>
> /* copy cmsg data temporarily out of the mbuf */
> tmp = malloc(control->m_len, M_TEMP, M_WAITOK);
> @@ -1008,7 +1018,8 @@ morespace:
> MCLGET(control, M_WAIT);
> if ((control->m_flags & M_EXT) == 0) {
> free(tmp, M_TEMP, control->m_len);
> - return (ENOBUFS); /* allocation failed */
> + error = ENOBUFS; /* allocation failed */
> + goto nospace;
> }
>
> /* copy the data back into the cluster */
> @@ -1049,10 +1060,11 @@ morespace:
> rp->flags = fdp->fd_ofileflags[fd] & UF_PLEDGED;
> rp--;
> if ((unp = fptounp(fp)) != NULL) {
> + rw_enter_write(&unp_lock);
> unp->unp_file = fp;
> unp->unp_msgcount++;
> + rw_exit_write(&unp_lock);
> }
> - unp_rights++;
> }
> fdpunlock(fdp);
> return (0);
> @@ -1064,11 +1076,18 @@ fail:
> for ( ; i > 0; i--) {
> rp++;
> fp = rp->fp;
> - if ((unp = fptounp(fp)) != NULL)
> + if ((unp = fptounp(fp)) != NULL) {
> + rw_enter_write(&unp_lock);
> unp->unp_msgcount--;
> + rw_exit_write(&unp_lock);
> + }
> FRELE(fp, p);
> - unp_rights--;
> }
> +
> +nospace:
> + rw_enter_write(&unp_lock);
> + unp_rights -= nfds;
> + rw_exit_write(&unp_lock);
>
> return (error);
> }
>
>
