Hello,
I'm reliably getting kernel crash on xtensa when CONFIG_SLUB
is selected and USE_SPLIT_PTLOCKS appears to be true (SMP=y,
NR_CPUS=4, DEBUG_SPINLOCK=n, DEBUG_LOCK_ALLOC=n).
This happens because spinlock_t ptl and struct page *first_page overlap
in the struct page. The following call chain makes allocation of order
3 and initializes first_page pointer in its 7 tail pages:
do_page_fault
handle_mm_fault
__pte_alloc
kmem_cache_alloc
__slab_alloc
new_slab
__alloc_pages_nodemask
get_page_from_freelist
prep_compound_page
Later pte_offset_map_lock is called with one of these tail pages
overwriting its first_page pointer:
do_fork
copy_process
dup_mm
copy_page_range
copy_pte_range
pte_alloc_map_lock
pte_offset_map_lock
Finally kmem_cache_free is called for that tail page, which calls
slab_free(s, virt_to_head_page(x),... but virt_to_head_page here
returns NULL, because the page's first_page pointer was overwritten
earlier:
exit_mmap
free_pgtables
free_pgd_range
free_pud_range
free_pmd_range
free_pte_range
pte_free
kmem_cache_free
slab_free
__slab_free
__slab_free touches NULL struct page, that's it.
Changing allocator to SLAB or enabling DEBUG_SPINLOCK
fixes that crash.
My question is, is CONFIG_SLUB supposed to work with
USE_SPLIT_PTLOCKS (and if yes what's wrong in my case)?
--
Thanks.
-- Max
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