Thanks for the remarks. On 05/14/2013 01:32 PM, Ming Lei wrote: > If the user buffer passed to driver A is mapped against file on the block > device, single thread 1 may still deadlock on the mutex A.
Good point, thanks. It is unlikely to ever be a use case for us, but still worth considering for the driver robustness. > It can't be avoided 100% with the memset() workaround since the user > buffer might be swapped out. Yep. We have swap disabled though, so this should be fine as a temporary workaround. > Looks there are some similar examples, one of them is b31ca3f5df( sysfs: > fix deadlock). > > ... > > Maybe it is good to document the lock usage, but the rule isn't much > complicated: if one lock may be held under mmap_sem, the lock can't be > held before copy_to/from_user(), :-) Ok. I see it is a known pitfall. Still, it would be nice if people could discover it not via a posteriori deadlocks debugging and lurking in list archives. :) -- 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/
