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Commit 487ad7ef authored by Ingo Molnar's avatar Ingo Molnar Committed by Linus Torvalds
Browse files

tty: fix BKL related leak and crash 



Enabling the BKL to be lockdep tracked uncovered the following
upstream kernel bug in the tty code, which caused a BKL
reference leak:

  ================================================
  [ BUG: lock held when returning to user space! ]
  ------------------------------------------------
  dmesg/3121 is leaving the kernel with locks still held!
  1 lock held by dmesg/3121:
   #0:  (kernel_mutex){--..}, at: [<c02f34d9>] opost+0x24/0x194

this might explain some of the atomicity warnings and crashes
that -tip tree testing has been experiencing since the BKL
was converted back to a spinlock.

Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 8568dae2

drivers/char/n_tty.c

+10 −3
Original line number Diff line number Diff line
@@ -282,16 +282,20 @@ static int opost(unsigned char c, struct tty_struct *tty) 
			if (O_ONLRET(tty))

				tty->column = 0;

			if (O_ONLCR(tty)) {

				if (space < 2)

				if (space < 2) {

					unlock_kernel();

					return -1;

				}

				tty_put_char(tty, '\r');

				tty->column = 0;

			}

			tty->canon_column = tty->column;

			break;

		case '\r':

			if (O_ONOCR(tty) && tty->column == 0)

			if (O_ONOCR(tty) && tty->column == 0) {

				unlock_kernel();

				return 0;

			}

			if (O_OCRNL(tty)) {

				c = '\n';

				if (O_ONLRET(tty))
@@ -303,10 +307,13 @@ static int opost(unsigned char c, struct tty_struct *tty) 
		case '\t':

			spaces = 8 - (tty->column & 7);

			if (O_TABDLY(tty) == XTABS) {

				if (space < spaces)

				if (space < spaces) {

					unlock_kernel();

					return -1;

				}

				tty->column += spaces;

				tty->ops->write(tty, "        ", spaces);

				unlock_kernel();

				return 0;

			}

			tty->column += spaces;