Serialize write() calls on TTYs.
Just like the old TTY layer, the current MPSAFE TTY layer does not make any attempt to serialize calls of write(). Data is copied into the kernel in 256 (TTY_STACKBUF) byte chunks. If a write() call occurs at the same time, the data may interleave. This is especially likely when the TTY starts blocking, because the output queue reaches the high watermark. I've implemented this by adding a new flag, TTY_BUSY_OUT, which is used to mark a TTY as having a thread stuck in write(). Because I don't want non-blocking processes to be possibly blocked by a sleeping thread, I'm still allowing it to bypass the protection. According to this message, the Linux kernel returns EAGAIN in such cases, but I think that's a little too restrictive: http://kerneltrap.org/index.php?q=mailarchive/linux-kernel/2007/5/2/85418/thread PR: kern/118287
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svn2git
2020-12-20 02:59:44 +00:00
svn path=/head/; revision=188487
@ -438,15 +438,28 @@ ttydev_write(struct cdev *dev, struct uio *uio, int ioflag)
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if (tp->t_termios.c_lflag & TOSTOP) {
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if (tp->t_termios.c_lflag & TOSTOP) {
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error = tty_wait_background(tp, curthread, SIGTTOU);
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error = tty_wait_background(tp, curthread, SIGTTOU);
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if (error) {
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if (error)
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tty_unlock(tp);
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goto done;
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return (error);
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}
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}
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}
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if (ioflag & IO_NDELAY && tp->t_flags & TF_BUSY_OUT) {
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/* Allow non-blocking writes to bypass serialization. */
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error = ttydisc_write(tp, uio, ioflag);
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error = ttydisc_write(tp, uio, ioflag);
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tty_unlock(tp);
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} else {
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/* Serialize write() calls. */
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while (tp->t_flags & TF_BUSY_OUT) {
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error = tty_wait(tp, &tp->t_bgwait);
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if (error)
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goto done;
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}
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tp->t_flags |= TF_BUSY_OUT;
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error = ttydisc_write(tp, uio, ioflag);
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tp->t_flags &= ~TF_BUSY_OUT;
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cv_broadcast(&tp->t_bgwait);
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}
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done: tty_unlock(tp);
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return (error);
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return (error);
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}
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}
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@ -1880,6 +1893,11 @@ static struct {
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{ TF_ZOMBIE, 'Z' },
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{ TF_ZOMBIE, 'Z' },
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{ TF_HOOK, 's' },
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{ TF_HOOK, 's' },
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/* Keep these together -> 'bi' and 'bo'. */
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{ TF_BUSY, 'b' },
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{ TF_BUSY_IN, 'i' },
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{ TF_BUSY_OUT, 'o' },
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{ 0, '\0'},
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{ 0, '\0'},
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};
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};
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@ -83,6 +83,9 @@ struct tty {
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#define TF_BYPASS 0x04000 /* Optimized input path. */
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#define TF_BYPASS 0x04000 /* Optimized input path. */
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#define TF_ZOMBIE 0x08000 /* Modem disconnect received. */
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#define TF_ZOMBIE 0x08000 /* Modem disconnect received. */
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#define TF_HOOK 0x10000 /* TTY has hook attached. */
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#define TF_HOOK 0x10000 /* TTY has hook attached. */
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#define TF_BUSY_IN 0x20000 /* Process busy in read() -- not supported. */
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#define TF_BUSY_OUT 0x40000 /* Process busy in write(). */
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#define TF_BUSY (TF_BUSY_IN|TF_BUSY_OUT)
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unsigned int t_revokecnt; /* (t) revoke() count. */
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unsigned int t_revokecnt; /* (t) revoke() count. */
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/* Buffering mechanisms. */
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/* Buffering mechanisms. */
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@ -206,6 +206,11 @@ block mode input routine in use
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connection lost
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connection lost
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.It s
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.It s
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i/o being snooped
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i/o being snooped
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.It b
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busy in
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.Xr read 2
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or
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.Xr write 2
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.El
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.El
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.Pp
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.Pp
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The
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The
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@ -315,6 +315,11 @@ static struct {
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{ TF_ZOMBIE, 'Z' },
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{ TF_ZOMBIE, 'Z' },
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{ TF_HOOK, 's' },
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{ TF_HOOK, 's' },
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/* Keep these together -> 'bi' and 'bo'. */
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{ TF_BUSY, 'b' },
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{ TF_BUSY_IN, 'i' },
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{ TF_BUSY_OUT, 'o' },
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{ 0, '\0'},
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{ 0, '\0'},
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};
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};
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