This is a note to let you know that I've just added the patch titled tty: teach the n_tty ICANON case about the new "cookie continuations" too to the 5.11-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: tty-teach-the-n_tty-icanon-case-about-the-new-cookie-continuations-too.patch and it can be found in the queue-5.11 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From d7fe75cbc23c7d225eee2ef04def239b6603dce7 Mon Sep 17 00:00:00 2001 From: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Date: Wed, 20 Jan 2021 15:43:38 -0800 Subject: tty: teach the n_tty ICANON case about the new "cookie continuations" too From: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> commit d7fe75cbc23c7d225eee2ef04def239b6603dce7 upstream. The ICANON case is a bit messy, since it has to look for the line ending, and has special code to then suppress line ending characters if they match the __DISABLED_CHAR. So it actually looks up the line ending even past the point where it knows it won't copy it to the result buffer. That said, apart from all those odd legacy N_TTY ICANON cases, the actual "should we continue copying" logic isn't really all that complicated or different from the non-canon case. In fact, the lack of "wait for at least N characters" arguably makes the repeat case slightly simpler. It really just boils down to "there's more of the line to be copied". So add the necessarily trivial logic, and now the N_TTY case will give long result lines even when in canon mode. Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- drivers/tty/n_tty.c | 26 +++++++++++++++++++------- 1 file changed, 19 insertions(+), 7 deletions(-) --- a/drivers/tty/n_tty.c +++ b/drivers/tty/n_tty.c @@ -2011,21 +2011,22 @@ static bool copy_from_read_buf(struct tt * read_tail published */ -static void canon_copy_from_read_buf(struct tty_struct *tty, +static bool canon_copy_from_read_buf(struct tty_struct *tty, unsigned char **kbp, size_t *nr) { struct n_tty_data *ldata = tty->disc_data; size_t n, size, more, c; size_t eol; - size_t tail; + size_t tail, canon_head; int found = 0; /* N.B. avoid overrun if nr == 0 */ if (!*nr) - return; + return false; - n = min(*nr + 1, smp_load_acquire(&ldata->canon_head) - ldata->read_tail); + canon_head = smp_load_acquire(&ldata->canon_head); + n = min(*nr + 1, canon_head - ldata->read_tail); tail = ldata->read_tail & (N_TTY_BUF_SIZE - 1); size = min_t(size_t, tail + n, N_TTY_BUF_SIZE); @@ -2069,7 +2070,11 @@ static void canon_copy_from_read_buf(str else ldata->push = 0; tty_audit_push(); + return false; } + + /* No EOL found - do a continuation retry if there is more data */ + return ldata->read_tail != canon_head; } /** @@ -2140,8 +2145,13 @@ static ssize_t n_tty_read(struct tty_str * termios_rwsem, and can just continue to copy data. */ if (*cookie) { - if (copy_from_read_buf(tty, &kb, &nr)) - return kb - kbuf; + if (ldata->icanon && !L_EXTPROC(tty)) { + if (canon_copy_from_read_buf(tty, &kb, &nr)) + return kb - kbuf; + } else { + if (copy_from_read_buf(tty, &kb, &nr)) + return kb - kbuf; + } /* No more data - release locks and stop retries */ n_tty_kick_worker(tty); @@ -2238,7 +2248,8 @@ static ssize_t n_tty_read(struct tty_str } if (ldata->icanon && !L_EXTPROC(tty)) { - canon_copy_from_read_buf(tty, &kb, &nr); + if (canon_copy_from_read_buf(tty, &kb, &nr)) + goto more_to_be_read; } else { /* Deal with packet mode. */ if (packet && kb == kbuf) { @@ -2256,6 +2267,7 @@ static ssize_t n_tty_read(struct tty_str * will release them when done. */ if (copy_from_read_buf(tty, &kb, &nr) && kb - kbuf >= minimum) { +more_to_be_read: remove_wait_queue(&tty->read_wait, &wait); *cookie = cookie; return kb - kbuf; Patches currently in stable-queue which might be from torvalds@xxxxxxxxxxxxxxxxxxxx are queue-5.11/tty-teach-the-n_tty-icanon-case-about-the-new-cookie-continuations-too.patch queue-5.11/tty-teach-n_tty-line-discipline-about-the-new-cookie-continuations.patch queue-5.11/tty-clean-up-legacy-leftovers-from-n_tty-line-discipline.patch queue-5.11/tty-fix-up-iterate_tty_read-eoverflow-handling.patch queue-5.11/mm-hugetlb.c-fix-unnecessary-address-expansion-of-pmd-sharing.patch queue-5.11/tty-fix-up-hung_up_tty_read-conversion.patch