Messages in this thread |  | | | Date | Fri, 9 Oct 2009 08:52:35 +0100 | | Subject | Re: select system call's implementation may have some bug, need your help and confirm !!! | | From | Alan Jenkins <> |
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On 10/9/09, wu Jianfeng <stormplayer@gmail.com> wrote: > A process may sleep for ever when he call select system call. > In detail, if the process was scheduled out just at the point it set > its state to TASK_INTERRUPTIBLE. > > The events that cause the process to be scheduled out is(in preempt kernel) > : > 1) time interrupt and the process's time slice is exhausted. > 2) an interrupt accured, and wake up another process with high priority. > > see the comments after "##" > > int do_select(int n, fd_set_bits *fds, s64 *timeout) > { > struct poll_wqueues table; > poll_table *wait; > int retval, i; > > rcu_read_lock(); > retval = max_select_fd(n, fds); > rcu_read_unlock(); > > if (retval < 0) > return retval; > n = retval; > > poll_initwait(&table); > wait = &table.pt; > if (!*timeout) > wait = NULL; > retval = 0; > for (;;) { > unsigned long *rinp, *routp, *rexp, *inp, *outp, *exp; > long __timeout; > > set_current_state(TASK_INTERRUPTIBLE); > ## here set the process state TASK_INTERRUPTIBLE > > ## if the process was scheduled out here, then the process will > never can be waked up, because it has not been attached to any file 's > wait queue.
I'm not sure about that, but if you look at the current code (e.g. in linus' git tree) you will see this code has been changed. Now set_current_state() is only called from poll_schedule_timeout(), and it won't suffer from the problem you suggested:
int poll_schedule_timeout(struct poll_wqueues *pwq, int state, ktime_t *expires, unsigned long slack) { int rc = -EINTR; set_current_state(state); if (!pwq->triggered) rc = schedule_hrtimeout_range(expires, slack, HRTIMER_MODE_ABS); __set_current_state(TASK_RUNNING);
I don't know the specific reason this was changed. Try looking at the git history if you're still curious.
Regards Alan
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