Re: Sending signals to a kernel thread, broken in 2.6.22

[Oleg Nesterov]

On 05/30, Oleg Nesterov wrote:
>
> Alan Stern wrote:
> >
> > The g_file_storage driver uses a kernel thread and communicates with
> > that thread in part by means of signals.  It also relies on the thread
> > receiving signals from userspace as an indication that the thread
> > should terminate.
> >
> > This was all working in 2.6.21, but as of 2.6.22-rc3 the signal
> > delivery mechanism (entirely within the kernel!) is no longer
> > functional.
> 
> I guess you mean drivers/usb/gadget/file_storage.c
> 
>       fsg_main_thread:
>               
>               siginitsetinv(&fsg->thread_signal_mask, SIGTERM | ...);
>               sigprocmask(SIG_SETMASK, &fsg->thread_signal_mask, NULL);
> 
> Yes?
> 
> Please look at
> 
>       change kernel threads to ignore signals instead of blocking them
>       commit: 10ab825bdef8df510f99c703a5a2d9b13a4e31a5
> 
> I think you can convert the code above to use allow_signal().

something like untested/uncompiled patch below, what do you think?

Oleg.

--- u/drivers/usb/gadget/file_storage.c~        2007-05-30 16:24:19.000000000 
+0400
+++ u/drivers/usb/gadget/file_storage.c 2007-05-30 16:29:21.000000000 +0400
@@ -686,7 +686,6 @@ struct fsg_dev {
        int                     thread_wakeup_needed;
        struct completion       thread_notifier;
        struct task_struct      *thread_task;
-       sigset_t                thread_signal_mask;
 
        int                     cmnd_size;
        u8                      cmnd[MAX_COMMAND_SIZE];
@@ -3277,8 +3276,7 @@ static void handle_exception(struct fsg_
        /* Clear the existing signals.  Anything but SIGUSR1 is converted
         * into a high-priority EXIT exception. */
        for (;;) {
-               sig = dequeue_signal_lock(current, &fsg->thread_signal_mask,
-                               &info);
+               sig = dequeue_signal_lock(current, &current->blocked, &info);
                if (!sig)
                        break;
                if (sig != SIGUSR1) {
@@ -3431,10 +3429,10 @@ static int fsg_main_thread(void *fsg_)
 
        /* Allow the thread to be killed by a signal, but set the signal mask
         * to block everything but INT, TERM, KILL, and USR1. */
-       siginitsetinv(&fsg->thread_signal_mask, sigmask(SIGINT) |
-                       sigmask(SIGTERM) | sigmask(SIGKILL) |
-                       sigmask(SIGUSR1));
-       sigprocmask(SIG_SETMASK, &fsg->thread_signal_mask, NULL);
+       allow_signal(SIGINT);
+       allow_signal(SIGTERM);
+       allow_signal(SIGKILL);
+       allow_signal(SIGUSR1);
 
        /* Arrange for userspace references to be interpreted as kernel
         * pointers.  That way we can pass a kernel pointer to a routine

-
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