Messages in this thread | | | Date | Wed, 28 Sep 2022 14:49:02 +0900 | From | Hyeonggon Yoo <> | Subject | Re: amusing SLUB compaction bug when CC_OPTIMIZE_FOR_SIZE |
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On Tue, Sep 27, 2022 at 10:16:35PM -0700, Hugh Dickins wrote: > It's a bug in linux-next, but taking me too long to identify which > commit is "to blame", so let me throw it over to you without more > delay: I think __PageMovable() now needs to check !PageSlab(). > > I had made a small experimental change somewhere, rebuilt and rebooted, > was not surprised to crash once swapping and compaction came in, > but was surprised to find the crash in isolate_movable_page(), > called by compaction's isolate_migratepages_block(). > > page->mapping was ffffffff811303aa, which qualifies as __PageMovable(), > which expects struct movable_operations at page->mapping minus low bits. > But ffffffff811303aa was the address of SLUB's rcu_free_slab(): I have > CONFIG_CC_OPTIMIZE_FOR_SIZE=y, so function addresses may have low bits set. > > Over to you! Thanks, > Hugh
Wow, didn't expect this. Thank you for report!
That should be due to commit 65505d1f2338e7 ("mm/sl[au]b: rearrange struct slab fields to allow larger rcu_head") as now rcu_head can use some bits that shares with mapping.
Hmm IMO we have two choices...
1. simply drop the commit as it's only for debugging (RCU folks may not like [1]) 2. make __PageMovable() to use true page flag, with approach [2])
[1] https://lore.kernel.org/all/85afd876-d8bb-0804-b2c5-48ed3055e702@joelfernandes.org/ [2] https://lore.kernel.org/linux-mm/20220919125708.276864-1-42.hyeyoo@gmail.com/
Thanks!
-- Thanks, Hyeonggon
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