Messages in this thread | | | Date | Tue, 18 Sep 2018 15:43:47 +0200 | From | Greg Kroah-Hartman <> | Subject | Re: [PATCHv5 2/7] tty/ldsem: Wake up readers after timed out down_write() |
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On Tue, Sep 18, 2018 at 12:52:53AM +0100, Dmitry Safonov wrote: > ldsem_down_read() will sleep if there is pending writer in the queue. > If the writer times out, readers in the queue should be woken up, > otherwise they may miss a chance to acquire the semaphore until the last > active reader will do ldsem_up_read(). > > There was a couple of reports where there was one active reader and > other readers soft locked up: > Showing all locks held in the system: > 2 locks held by khungtaskd/17: > #0: (rcu_read_lock){......}, at: watchdog+0x124/0x6d1 > #1: (tasklist_lock){.+.+..}, at: debug_show_all_locks+0x72/0x2d3 > 2 locks held by askfirst/123: > #0: (&tty->ldisc_sem){.+.+.+}, at: ldsem_down_read+0x46/0x58 > #1: (&ldata->atomic_read_lock){+.+...}, at: n_tty_read+0x115/0xbe4 > > Prevent readers wait for active readers to release ldisc semaphore. > > Link: lkml.kernel.org/r/<20171121132855.ajdv4k6swzhvktl6@wfg-t540p.sh.intel.com> > Link: lkml.kernel.org/r/<20180907045041.GF1110@shao2-debian> > Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> > Cc: Jiri Slaby <jslaby@suse.com> > Cc: Peter Zijlstra <peterz@infradead.org> > Reported-by: kernel test robot <rong.a.chen@intel.com> > Signed-off-by: Dmitry Safonov <dima@arista.com> > ---
Why isn't this ok for the stable trees?
thanks,
greg k-h
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