On 02/18, Rafael J. Wysocki wrote: > > On Sunday, 18 February 2007 12:32, Oleg Nesterov wrote: > > On 02/18, Rafael J. Wysocki wrote: > > > > > > On Sunday, 18 February 2007 00:42, Oleg Nesterov wrote: > > > > On 02/17, Rafael J. Wysocki wrote: > > > > > > > > > > On Saturday, 17 February 2007 22:34, Oleg Nesterov wrote: > > > > > > > > > > > > static inline int is_user_space(struct task_struct *p) > > > > > > { > > > > > > return p->mm && !(p->flags & PF_BORROWED_MM); > > > > > > } > > > > > > > > > > > > This doesn't look right. First, an exiting task has ->mm == NULL > > > > > > after > > > > > > do_exit()->exit_mm(). Probably not a problem. However, > > > > > > PF_BORROWED_MM > > > > > > check is racy without task_lock(), so we can have a false positive > > > > > > as > > > > > > well. Is it ok? We can freeze aio_wq prematurely. > > > > > > > > > > Right now aio_wq is not freezeable (PF_NOFREEZE). > > > > > > > > Right now yes, but we are going to change this? > > > > > > Well, is there any more reliable (and not racy) method of differentiating > > > between kernel threads and user space processes? > > > > Not that I know of. At least, we can take task_lock() to really rule out > > kernel threads at FREEZER_USER_SPACE stage. > > Something like this?
I think yes, as a first step. In the long term, I think it would be really nice to have CLONE_KERNEL_THREAD (filtered out in sys_clone). This also allows us to cleanup copy_process(). For example, we can then introduce CLONE_UNHASHED (currently denoted as pid==0) and kill the ugly "int pid" copy_process's parameter. Oleg. > --- > kernel/power/process.c | 8 +++++++- > 1 file changed, 7 insertions(+), 1 deletion(-) > > Index: linux-2.6.20-mm2/kernel/power/process.c > =================================================================== > --- linux-2.6.20-mm2.orig/kernel/power/process.c > +++ linux-2.6.20-mm2/kernel/power/process.c > @@ -8,6 +8,7 @@ > > #undef DEBUG > > +#include <linux/sched.h> > #include <linux/smp_lock.h> > #include <linux/interrupt.h> > #include <linux/suspend.h> > @@ -92,7 +93,12 @@ static void cancel_freezing(struct task_ > > static inline int is_user_space(struct task_struct *p) > { > - return p->mm && !(p->flags & PF_BORROWED_MM); > + int ret; > + > + task_lock(p); > + ret = p->mm && !(p->flags & PF_BORROWED_MM); > + task_unlock(p); > + return ret; > } > > static unsigned int try_to_freeze_tasks(int freeze_user_space) - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/