search for: head_mask

...gh bytes (head really >> needs to be high to work, if it's in the low byte(s) the xadd would >> overflow from head into tail which would be wrong). > > Unfortunately xadd could result in head overflow as tail is high. xadd can overflow, but is this really a problem? # define HEAD_MASK (TICKET_SLOWPATH_FLAG-1) ... unlock_again: val = xadd((&lock->ticket.head_tail, TICKET_LOCK_INC); if (unlikely(!(val & HEAD_MASK))) { /* overflow. we inadvertently incremented the tail word. * tail's lsb is TICKET_SLOWPATH_FLAG. * Increment inverted this bit, fix it u...

...gh bytes (head really >> needs to be high to work, if it's in the low byte(s) the xadd would >> overflow from head into tail which would be wrong). > > Unfortunately xadd could result in head overflow as tail is high. xadd can overflow, but is this really a problem? # define HEAD_MASK (TICKET_SLOWPATH_FLAG-1) ... unlock_again: val = xadd((&lock->ticket.head_tail, TICKET_LOCK_INC); if (unlikely(!(val & HEAD_MASK))) { /* overflow. we inadvertently incremented the tail word. * tail's lsb is TICKET_SLOWPATH_FLAG. * Increment inverted this bit, fix it u...

On Mon, Feb 9, 2015 at 4:02 AM, Peter Zijlstra <peterz at infradead.org> wrote: > On Mon, Feb 09, 2015 at 03:04:22PM +0530, Raghavendra K T wrote: >> So we have 3 choices, >> 1. xadd >> 2. continue with current approach. >> 3. a read before unlock and also after that. > > For the truly paranoid we have probe_kernel_address(), suppose the lock > was in

On Mon, Feb 9, 2015 at 4:02 AM, Peter Zijlstra <peterz at infradead.org> wrote: > On Mon, Feb 09, 2015 at 03:04:22PM +0530, Raghavendra K T wrote: >> So we have 3 choices, >> 1. xadd >> 2. continue with current approach. >> 3. a read before unlock and also after that. > > For the truly paranoid we have probe_kernel_address(), suppose the lock > was in