tty: Serialize tcflow() with other tty flow control changes
Use newly-introduced tty->flow_lock to serialize updates to tty->flow_stopped (via tcflow()) and with concurrent tty flow control changes from other sources. Merge the storage for ->stopped and ->flow_stopped, now that both flags are serialized by ->flow_lock. The padding bits are necessary to force the compiler to allocate the type specified; otherwise, gcc will ignore the type specifier and allocate the minimum number of bytes necessary to store the bitfield. In turn, this would allow Alpha EV4 and EV5 cpus to corrupt adjacent byte storage because those cpus use RMW to store byte and short data. gcc versions < 4.7.2 will also corrupt storage adjacent to bitfields smaller than unsigned long on ia64, ppc64, hppa64 and sparc64, thus requiring more than unsigned int storage (which would otherwise be sufficient to workaround the Alpha non-atomic byte/short storage problem). Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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@ -1177,16 +1177,20 @@ int n_tty_ioctl_helper(struct tty_struct *tty, struct file *file,
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return retval;
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switch (arg) {
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case TCOOFF:
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spin_lock_irq(&tty->flow_lock);
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if (!tty->flow_stopped) {
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tty->flow_stopped = 1;
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stop_tty(tty);
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__stop_tty(tty);
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}
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spin_unlock_irq(&tty->flow_lock);
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break;
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case TCOON:
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spin_lock_irq(&tty->flow_lock);
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if (tty->flow_stopped) {
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tty->flow_stopped = 0;
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start_tty(tty);
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__start_tty(tty);
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}
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spin_unlock_irq(&tty->flow_lock);
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break;
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case TCIOFF:
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if (STOP_CHAR(tty) != __DISABLED_CHAR)
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@ -262,8 +262,9 @@ struct tty_struct {
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unsigned long flags;
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int count;
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struct winsize winsize; /* winsize_mutex */
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int stopped; /* flow_lock */
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int flow_stopped;
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unsigned long stopped:1, /* flow_lock */
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flow_stopped:1,
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unused:62;
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int hw_stopped;
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int packet;
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unsigned char ctrl_status; /* ctrl_lock */
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