[MAJOR] spec I/O: fix allocations of spec entries for an FD

Under some circumstances, it was possible with speculative I/O to
reallocate multiple entries for the same FD if an fd_{set,clr,set}
or fd_{clr,set,clr} sequences were performed before a schedule.

Fix this by keeping a an allocation flag for each fd.

diff --git a/src/ev_sepoll.c b/src/ev_sepoll.c
index 852577caa6e5837ed3917e1036e6eab9d752770e..c58bf5394969f1509739ec719a341a2bfdfe8be5 100644 (file)
--- a/src/ev_sepoll.c
+++ b/src/ev_sepoll.c
@@ -115,7 +115,7 @@ static _syscall4 (int, epoll_wait, int, epfd, struct epoll_event *, events, int,
  * FIXME: should be a bit field */
 struct fd_status {
        unsigned int e:4;       // read and write events status.
-       unsigned int s:28;      // Position in spec list. Should be last.
+       unsigned int s1:28;     // Position in spec list+1. 0=not in list. Should be last.
 };
 
 static int nbspec = 0;          // current size of the spec list
@@ -135,27 +135,37 @@ static struct epoll_event ev;
 
 REGPRM1 static void alloc_spec_entry(const int fd)
 {
-       if (fd_list[fd].e & FD_EV_RW_SL)
+       if (fd_list[fd].s1)
                return;
-       fd_list[fd].s = nbspec;
-       spec_list[nbspec++] = fd;
+       fd_list[fd].s1 = nbspec + 1;
+       spec_list[nbspec] = fd;
+       nbspec++;
 }
 
-/* removes entry <pos> from the spec list and replaces it with the last one.
- * The fd_list is adjusted to match the back reference if needed.
+/* Removes entry used by fd <fd> from the spec list and replaces it with the
+ * last one. The fd_list is adjusted to match the back reference if needed.
+ * If the fd has no entry assigned, return immediately.
  */
-REGPRM1 static void delete_spec_entry(const int pos)
+REGPRM1 static void release_spec_entry(int fd)
 {
-       int fd;
+       unsigned int pos;
+
+       pos = fd_list[fd].s1;
+       if (!pos)
+               return;
+
+       fd_list[fd].s1 = 0;
+       pos--;
+       /* we have spec_list[pos]==fd */
 
        nbspec--;
        if (pos == nbspec)
                return;
 
-       /* we replace current FD by the highest one */
+       /* we replace current FD by the highest one, which may sometimes be the same */
        fd = spec_list[nbspec];
+       fd_list[fd].s1 = pos + 1;
        spec_list[pos] = fd;
-       fd_list[fd].s = pos;
 }
 
 /*
@@ -234,7 +244,7 @@ REGPRM1 static void __fd_rem(int fd)
 REGPRM1 static void __fd_clo(int fd)
 {
        if (fd_list[fd].e & FD_EV_RW_SL)
-               delete_spec_entry(fd_list[fd].s);
+               release_spec_entry(fd);
        fd_list[fd].e &= ~(FD_EV_MASK);
 }
 
@@ -346,7 +356,7 @@ REGPRM2 static void _do_poll(struct poller *p, struct timeval *exp)
                        /* This fd switched to combinations of either WAIT or
                         * IDLE. It must be removed from the spec list.
                         */
-                       delete_spec_entry(spec_idx);
+                       release_spec_entry(fd);
                        continue;
                }
        }