Messages in this thread | | | Date | Thu, 10 Jan 2013 13:56:07 +0800 | From | Tang Chen <> | Subject | Re: [PATCH v6 02/15] memory-hotplug: check whether all memory blocks are offlined or not when removing memory |
| |
Hi Andrew,
On 01/10/2013 07:11 AM, Andrew Morton wrote: > On Wed, 9 Jan 2013 17:32:26 +0800 > Tang Chen<tangchen@cn.fujitsu.com> wrote: > >> We remove the memory like this: >> 1. lock memory hotplug >> 2. offline a memory block >> 3. unlock memory hotplug >> 4. repeat 1-3 to offline all memory blocks >> 5. lock memory hotplug >> 6. remove memory(TODO) >> 7. unlock memory hotplug >> >> All memory blocks must be offlined before removing memory. But we don't hold >> the lock in the whole operation. So we should check whether all memory blocks >> are offlined before step6. Otherwise, kernel maybe panicked. > > Well, the obvious question is: why don't we hold lock_memory_hotplug() > for all of steps 1-4? Please send the reasons for this in a form which > I can paste into the changelog.
In the changelog form:
Offlining a memory block and removing a memory device can be two different operations. Users can just offline some memory blocks without removing the memory device. For this purpose, the kernel has held lock_memory_hotplug() in __offline_pages(). To reuse the code for memory hot-remove, we repeat step 1-3 to offline all the memory blocks, repeatedly lock and unlock memory hotplug, but not hold the memory hotplug lock in the whole operation.
> > > Actually, I wonder if doing this would fix a race in the current > remove_memory() repeat: loop. That code does a > find_memory_block_hinted() followed by offline_memory_block(), but > afaict find_memory_block_hinted() only does a get_device(). Is the > get_device() sufficiently strong to prevent problems if another thread > concurrently offlines or otherwise alters this memory_block's state?
I think we already have memory_block->state_mutex to protect the concurrently changing of memory_block's state.
The find_memory_block_hinted() here is to find the memory_block corresponding to the memory section we are dealing with.
Thanks. :)
>
| |