Messages in this thread | | | Date | Thu, 21 Jan 2010 11:18:50 -0800 | From | David Daney <> | Subject | Re: Lots of bugs with current->state = TASK_*INTERRUPTIBLE |
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Steven Rostedt wrote: > Peter Zijlstra and I were doing a look over of places that assign > current->state = TASK_*INTERRUPTIBLE, by simply looking at places with: > > $ git grep -A1 'state[[:space:]]*=[[:space:]]*TASK_[^R]' > > and it seems there are quite a few places that looks like bugs. To be on > the safe side, everything outside of a run queue lock that sets the > current state to something other than TASK_RUNNING (or dead) should be > using set_current_state(). > > current->state = TASK_INTERRUPTIBLE; > schedule(); > > is probably OK, but it would not hurt to be consistent. Here's a few > examples of likely bugs: > [...]
This may be a bit off topic, but exactly which type of barrier should set_current_state() be implying?
On MIPS, set_mb() (which is used by set_current_state()) has a full mb().
Some MIPS based processors have a much lighter weight wmb(). Could wmb() be used in place of mb() here?
If not, an explanation of the required memory ordering semantics here would be appreciated.
I know the documentation says:
set_current_state() includes a barrier so that the write of current->state is correctly serialised wrt the caller's subsequent test of whether to actually sleep:
set_current_state(TASK_UNINTERRUPTIBLE); if (do_i_need_to_sleep()) schedule();
Since the current CPU sees the memory accesses in order, what can be happening on other CPUs that would require a full mb()?
Thanks, David Daney
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