BUG/MEDIUM: fd: maintain a per-thread update mask

Since the fd update tables are per-thread, we need to have a bit per
thread to indicate whether an update exists, otherwise this can lead
to lost update events every time multiple threads want to update the
same FD. In practice *for now*, it only happens at start time when
listeners are enabled and ask for polling after facing their first
EAGAIN. But since the pollers are still shared, a lost event is still
recovered by a neighbor thread. This will not reliably work anymore
with per-thread pollers, where it has been observed a few times on
startup that a single-threaded listener would not always accept
incoming connections upon startup.

It's worth noting that during this code review it appeared that the
"new" flag in the fdtab isn't used anymore.

This fix should be backported to 1.8.

include/proto/fd.h

@@ -99,10 +99,10 @@ void fd_process_cached_events();
  */
 static inline void updt_fd_polling(const int fd)
 {
-	if (fdtab[fd].updated)
+	if (fdtab[fd].update_mask & tid_bit)
 		/* already scheduled for update */
 		return;
-	fdtab[fd].updated = 1;
+	fdtab[fd].update_mask |= tid_bit;
 	fd_updt[fd_nbupdt++] = fd;
 }
 
@@ -400,7 +400,7 @@ static inline void fd_insert(int fd, unsigned long thread_mask)
 	HA_SPIN_LOCK(FD_LOCK, &fdtab[fd].lock);
 	fdtab[fd].ev = 0;
 	fdtab[fd].new = 1;
-	fdtab[fd].updated = 0;
+	fdtab[fd].update_mask &= ~tid_bit;
 	fdtab[fd].linger_risk = 0;
 	fdtab[fd].cloned = 0;
 	fdtab[fd].cache = 0;

include/types/fd.h

@@ -94,13 +94,13 @@ enum fd_states {
 struct fdtab {
 	__decl_hathreads(HA_SPINLOCK_T lock);
 	unsigned long thread_mask;           /* mask of thread IDs authorized to process the task */
+	unsigned long update_mask;           /* mask of thread IDs having an update for fd */
 	void (*iocb)(int fd);                /* I/O handler */
 	void *owner;                         /* the connection or listener associated with this fd, NULL if closed */
 	unsigned int  cache;                 /* position+1 in the FD cache. 0=not in cache. */
 	unsigned char state;                 /* FD state for read and write directions (2*3 bits) */
 	unsigned char ev;                    /* event seen in return of poll() : FD_POLL_* */
 	unsigned char new:1;                 /* 1 if this fd has just been created */
-	unsigned char updated:1;             /* 1 if this fd is already in the update list */
 	unsigned char linger_risk:1;         /* 1 if we must kill lingering before closing */
 	unsigned char cloned:1;              /* 1 if a cloned socket, requires EPOLL_CTL_DEL on close */
 };

src/cli.c

@@ -794,7 +794,7 @@ static int cli_io_handler_show_fd(struct appctx *appctx)
 			li = fdt.owner;
 
 		chunk_printf(&trash,
-			     "  %5d : st=0x%02x(R:%c%c%c W:%c%c%c) ev=0x%02x(%c%c%c%c%c) [%c%c%c%c] cache=%u owner=%p iocb=%p(%s) tmask=0x%lx",
+			     "  %5d : st=0x%02x(R:%c%c%c W:%c%c%c) ev=0x%02x(%c%c%c%c%c) [%c%c%c] cache=%u owner=%p iocb=%p(%s) tmask=0x%lx umask=0x%lx",
 			     fd,
 			     fdt.state,
 			     (fdt.state & FD_EV_POLLED_R) ? 'P' : 'p',
@@ -810,7 +810,6 @@ static int cli_io_handler_show_fd(struct appctx *appctx)
 			     (fdt.ev & FD_POLL_PRI) ? 'P' : 'p',
 			     (fdt.ev & FD_POLL_IN)  ? 'I' : 'i',
 			     fdt.new ? 'N' : 'n',
-			     fdt.updated ? 'U' : 'u',
 			     fdt.linger_risk ? 'L' : 'l',
 			     fdt.cloned ? 'C' : 'c',
 			     fdt.cache,
@@ -820,7 +819,7 @@ static int cli_io_handler_show_fd(struct appctx *appctx)
 			     (fdt.iocb == dgram_fd_handler) ? "dgram_fd_handler" :
 			     (fdt.iocb == listener_accept)  ? "listener_accept" :
 			     "unknown",
-			     fdt.thread_mask);
+			     fdt.thread_mask, fdt.update_mask);
 
 		if (fdt.iocb == conn_fd_handler) {
 			chunk_appendf(&trash, " cflg=0x%08x", conn_flags);

src/ev_epoll.c

@@ -74,7 +74,7 @@ REGPRM2 static void _do_poll(struct poller *p, int exp)
 		}
 
 		HA_SPIN_LOCK(FD_LOCK, &fdtab[fd].lock);
-		fdtab[fd].updated = 0;
+		fdtab[fd].update_mask &= ~tid_bit;
 		fdtab[fd].new = 0;
 
 		eo = fdtab[fd].state;

src/ev_kqueue.c

@@ -53,7 +53,7 @@ REGPRM2 static void _do_poll(struct poller *p, int exp)
 		}
 
 		HA_SPIN_LOCK(FD_LOCK, &fdtab[fd].lock);
-		fdtab[fd].updated = 0;
+		fdtab[fd].update_mask &= ~tid_bit;
 		fdtab[fd].new = 0;
 
 		eo = fdtab[fd].state;

src/ev_poll.c

@@ -79,7 +79,7 @@ REGPRM2 static void _do_poll(struct poller *p, int exp)
 		}
 
 		HA_SPIN_LOCK(FD_LOCK, &fdtab[fd].lock);
-		fdtab[fd].updated = 0;
+		fdtab[fd].update_mask &= ~tid_bit;
 		fdtab[fd].new = 0;
 
 		eo = fdtab[fd].state;

src/ev_select.c

@@ -61,7 +61,7 @@ REGPRM2 static void _do_poll(struct poller *p, int exp)
 		}
 
 		HA_SPIN_LOCK(FD_LOCK, &fdtab[fd].lock);
-		fdtab[fd].updated = 0;
+		fdtab[fd].update_mask &= ~tid_bit;
 		fdtab[fd].new = 0;
 
 		eo = fdtab[fd].state;

src/fd.c

@@ -199,7 +199,7 @@ static void fd_dodelete(int fd, int do_close)
 	port_range_release_port(fdinfo[fd].port_range, fdinfo[fd].local_port);
 	fdinfo[fd].port_range = NULL;
 	fdtab[fd].owner = NULL;
-	fdtab[fd].updated = 0;
+	fdtab[fd].update_mask &= ~tid_bit;
 	fdtab[fd].new = 0;
 	fdtab[fd].thread_mask = 0;
 	if (do_close)

src/stream.c

@@ -2906,7 +2906,7 @@ static int stats_dump_full_strm_to_buffer(struct stream_interface *si, struct st
 			              conn->handle.fd,
 			              conn->handle.fd >= 0 ? fdtab[conn->handle.fd].state : 0,
 			              conn->handle.fd >= 0 ? fdtab[conn->handle.fd].cache : 0,
-			              conn->handle.fd >= 0 ? fdtab[conn->handle.fd].updated : 0,
+			              conn->handle.fd >= 0 ? !!(fdtab[conn->handle.fd].update_mask & tid_bit) : 0,
 				      conn->handle.fd >= 0 ? fdtab[conn->handle.fd].thread_mask: 0);
 		}
 		else if ((tmpctx = objt_appctx(strm->si[0].end)) != NULL) {
@@ -2939,7 +2939,7 @@ static int stats_dump_full_strm_to_buffer(struct stream_interface *si, struct st
 			              conn->handle.fd,
 			              conn->handle.fd >= 0 ? fdtab[conn->handle.fd].state : 0,
 			              conn->handle.fd >= 0 ? fdtab[conn->handle.fd].cache : 0,
-			              conn->handle.fd >= 0 ? fdtab[conn->handle.fd].updated : 0,
+			              conn->handle.fd >= 0 ? !!(fdtab[conn->handle.fd].update_mask & tid_bit) : 0,
 				      conn->handle.fd >= 0 ? fdtab[conn->handle.fd].thread_mask: 0);
 		}
 		else if ((tmpctx = objt_appctx(strm->si[1].end)) != NULL) {