On (05/29/15 23:54), Minchan Kim wrote: > I think the problem is caused from weired feature "reset" of zram. agree. > Until a while ago, we didn't have hot_add/del feature so we should > use custom reset function but now we have hot/add feature. > So reset is logically same feature(ie, reset = hot_remove+hot_add > but remains same device id). > hm, sounds interesting, but I think it will end up being tricky. zram_remove() will be called from device's sysfs node (now we call it from zram_control sysfs class node, makes a huge difference). sysfs locks the node until node's read/write handler returns back, so zram_remove() will be called with lock(s_active#XXX) being locked (we had a lockdep splat with these locks recently), while zram_remove()->sysfs_remove_group() will once again attempt to lock this node (the very same lock(s_active#XXX)). in other words, we cannot fully remove zram device from its sysfs attr. and I don't want to add any bool flags to zram_remove() and zram_add() indicating that this is a "partial" device remove: don't delete device's sysfs group in remove() and don't create it in add(). doing reset from zram_control is easy, for sure: lock idr mutex, do zram_remove() and zram_add() unlock idr lock. `echo ID > /sys/.../zram_control/reset` no need to modify remove()/add() -- idr will pick up just released idx, so device_id will be preserved. but it'll be hard to drop the per-device `reset` attr and to make it a zram_control attr. things would have been much simpler if all of zram users were also zramctl users. zramctl, from this point of view, lets us change zram interfaces easily -- we merely need to teach/modify zramctl, the rest is transparent. -ss -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>