Hi Qi, Thanks for the fix. I will test it as well as I can. On Wed, Feb 12, 2025 at 7:41 AM Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx> wrote: > > When update_mmu_cache_range() is called by update_mmu_cache(), the vmf > parameter is NULL, which will cause a NULL pointer dereference issue in > adjust_pte(): > > Unable to handle kernel NULL pointer dereference at virtual address 00000030 when read > Hardware name: Atmel AT91SAM9 > PC is at update_mmu_cache_range+0x1e0/0x278 > LR is at pte_offset_map_rw_nolock+0x18/0x2c > Call trace: > update_mmu_cache_range from remove_migration_pte+0x29c/0x2ec > remove_migration_pte from rmap_walk_file+0xcc/0x130 > rmap_walk_file from remove_migration_ptes+0x90/0xa4 > remove_migration_ptes from migrate_pages_batch+0x6d4/0x858 > migrate_pages_batch from migrate_pages+0x188/0x488 > migrate_pages from compact_zone+0x56c/0x954 > compact_zone from compact_node+0x90/0xf0 > compact_node from kcompactd+0x1d4/0x204 > kcompactd from kthread+0x120/0x12c > kthread from ret_from_fork+0x14/0x38 > Exception stack(0xc0d8bfb0 to 0xc0d8bff8) > > To fix it, do not rely on whether 'ptl' is equal to decide whether to hold > the pte lock, but decide it by whether CONFIG_SPLIT_PTE_PTLOCKS is > enabled. In addition, if two vmas map to the same PTE page, there is no > need to hold the pte lock again, otherwise a deadlock will occur. Just add > the need_lock parameter to let adjust_pte() know this information. > > Reported-by: Ezra Buehler <ezra@xxxxxxxx> Perhaps a detail but, maybe better use "Ezra Buehler <ezra.buehler@xxxxxxxxxxxxxxxxxx>" here. Cheers, Ezra.
