On Wed, Mar 20, 2013 at 01:20:43PM -0400, Peter Hurley wrote: > As Ilya Zykov identified in his patch 'PROBLEM: Race condition in > tty buffer's function flush_to_ldisc()', a race condition exists > which allows a parallel flush_to_ldisc() to flush and free the tty > flip buffers while those buffers are in-use. For example, > > CPU 0 | CPU 1 | CPU 2 > | flush_to_ldisc() | > | grab spin lock | > tty_buffer_flush() | | flush_to_ldisc() > wait for spin lock | | wait for spin lock > | if (!test_and_set_bit(TTYP_FLUSHING)) | > | while (next flip buffer) | > | ... | > | drop spin lock | > grab spin lock | | > if (test_bit(TTYP_FLUSHING)) | | > set_bit(TTYP_FLUSHPENDING) | receive_buf() | > drop spin lock | | > | | grab spin lock > | | if (!test_and_set_bit(TTYP_FLUSHING)) > | | if (test_bit(TTYP_FLUSHPENDING)) > | | __tty_buffer_flush() > > CPU 2 has just flushed and freed all tty flip buffers while CPU 1 is > transferring data from the head flip buffer. > > The original patch was rejected under the assumption that parallel > flush_to_ldisc() was not possible. Because of necessary changes to > the workqueue api, work items can execute in parallel on SMP. > > This patch differs slightly from the original patch by testing for > a pending flush _after_ each receive_buf(), since TTYP_FLUSHPENDING > can only be set while the lock is dropped around receive_buf(). > > Reported-by: Ilya Zykov <linux@xxxxxxx> > Signed-off-by: Peter Hurley <peter@xxxxxxxxxxxxxxxxxx> > --- > drivers/tty/tty_buffer.c | 22 ++++++++++------------ > 1 file changed, 10 insertions(+), 12 deletions(-) What tree is this against? Does it need your other larger set of ldisc patches, or can it be applied without it? confused, greg k-h -- To unsubscribe from this list: send the line "unsubscribe linux-serial" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
