Messages in this thread | | | Date | Wed, 4 Apr 2018 17:43:16 +0200 | From | Greg KH <> | Subject | Re: [PATCH] locking/qrwlock: Give priority to readers with irqs disabled to prevent deadlock |
| |
On Wed, Apr 04, 2018 at 06:24:39PM +0300, Kirill Tkhai wrote: > The following situation leads to deadlock: > > [task 1] [task 2] [task 3] > kill_fasync() mm_update_next_owner() copy_process() > spin_lock_irqsave(&fa->fa_lock) read_lock(&tasklist_lock) write_lock_irq(&tasklist_lock) > send_sigio() <IRQ> ... > read_lock(&fown->lock) kill_fasync() ... > read_lock(&tasklist_lock) spin_lock_irqsave(&fa->fa_lock) ... > > Task 1 can't acquire read locked tasklist_lock, since there is > already task 3 expressed its wish to take the lock exclusive. > Task 2 holds the read locked lock, but it can't take the spin lock. > > The patch makes queued_read_lock_slowpath() to give task 1 the same > priority as it was an interrupt handler, and to take the lock > dispite of task 3 is waiting it, and this prevents the deadlock. > It seems there is no better way to detect such the situations, > also in general it's not good to wait so long for readers with > interrupts disabled, since read_lock may nest with another locks > and delay the system. > > Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com> > --- > kernel/locking/qrwlock.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-)
<formletter>
This is not the correct way to submit patches for inclusion in the stable kernel tree. Please read: https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html for how to do this properly.
</formletter>
| |