Messages in this thread | | | Subject | Re: [RFC PATCH] introduce sys_membarrier(): process-wide memory barrier | From | Steven Rostedt <> | Date | Sun, 10 Jan 2010 06:50:09 -0500 |
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On Sat, 2010-01-09 at 21:25 -0800, Paul E. McKenney wrote: > On Sat, Jan 09, 2010 at 09:12:58PM -0500, Steven Rostedt wrote:
> > > < user space > > > > > > > < misses that CPU 2 is in rcu section > > > > > > > If the TLB flush misses that CPU 2 has a threaded task, and does not > > flush CPU 2s TLB, it can also risk the same type of crash. > > But isn't the VM's locking helping us out in that case? > > > > [CPU 2's ->curr update now visible] > > > > > > [CPU 2's rcu_read_lock() store now visible] > > > > > > free(obj); > > > > > > use_object(obj); <=== crash! > > > > > > > Think about it. If you change a process mmap, say you updated a mmap of > > a file by flushing out one page and replacing it with another. If the > > above missed sending to CPU 2, then CPU 2 may still be accessing the old > > page of the file, and not the new one. > > > > I think this may be the safe bet. > > You might well be correct that we can access that bitmap locklessly, > but there are additional things (like the loading of the arch-specific > page-table register) that are likely to be helping in the VM case, but > not necessarily helping in this case.
Then perhaps the sys_membarrier() should just do a flush_tlb()? That should guarantee the synchronization, right?
-- Steve
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