RFE: minimze ebitmap serialization #66
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stephensmalley
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May 2, 2024
Florian reported the following kernel NULL pointer dereference issue on a BCM7250 board: [ 2.829744] Unable to handle kernel NULL pointer dereference at virtual address 0000000c when read [ 2.838740] [0000000c] *pgd=80000000004003, *pmd=00000000 [ 2.844178] Internal error: Oops: 206 [SELinuxProject#1] SMP ARM [ 2.848990] Modules linked in: [ 2.852061] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 6.8.0-next-20240305-gd95fcdf4961d SELinuxProject#66 [ 2.860436] Hardware name: Broadcom STB (Flattened Device Tree) [ 2.866371] PC is at brcmnand_read_by_pio+0x180/0x278 [ 2.871449] LR is at __wait_for_common+0x9c/0x1b0 [ 2.876178] pc : [<c094b6cc>] lr : [<c0e66310>] psr: 60000053 [ 2.882460] sp : f0811a80 ip : 00000012 fp : 00000000 [ 2.887699] r10: 00000000 r9 : 00000000 r8 : c3790000 [ 2.892936] r7 : 00000000 r6 : 00000000 r5 : c35db440 r4 : ffe00000 [ 2.899479] r3 : f15cb814 r2 : 00000000 r1 : 00000000 r0 : 00000000 The issue only happens when dma mode is disabled or not supported on STB chip. The pio mode transfer calls brcmnand_read_data_bus function which dereferences ctrl->soc->read_data_bus. But the soc member in STB chip is NULL hence triggers the access violation. The function needs to check the soc pointer first. Fixes: 546e425 ("mtd: rawnand: brcmnand: Add BCMBCA read data bus interface") Reported-by: Florian Fainelli <[email protected]> Tested-by: Florian Fainelli <[email protected]> Signed-off-by: William Zhang <[email protected]> Signed-off-by: Miquel Raynal <[email protected]> Link: https://lore.kernel.org/linux-mtd/[email protected]
pcmoore
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Jul 29, 2024
…b folio A kernel crash was observed when migrating hugetlb folio: BUG: kernel NULL pointer dereference, address: 0000000000000008 PGD 0 P4D 0 Oops: Oops: 0002 [#1] PREEMPT SMP NOPTI CPU: 0 PID: 3435 Comm: bash Not tainted 6.10.0-rc6-00450-g8578ca01f21f #66 RIP: 0010:__folio_undo_large_rmappable+0x70/0xb0 RSP: 0018:ffffb165c98a7b38 EFLAGS: 00000097 RAX: fffffbbc44528090 RBX: 0000000000000000 RCX: 0000000000000000 RDX: ffffa30e000a2800 RSI: 0000000000000246 RDI: ffffa3153ffffcc0 RBP: fffffbbc44528000 R08: 0000000000002371 R09: ffffffffbe4e5868 R10: 0000000000000001 R11: 0000000000000001 R12: ffffa3153ffffcc0 R13: fffffbbc44468000 R14: 0000000000000001 R15: 0000000000000001 FS: 00007f5b3a716740(0000) GS:ffffa3151fc00000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000000000000008 CR3: 000000010959a000 CR4: 00000000000006f0 Call Trace: <TASK> __folio_migrate_mapping+0x59e/0x950 __migrate_folio.constprop.0+0x5f/0x120 move_to_new_folio+0xfd/0x250 migrate_pages+0x383/0xd70 soft_offline_page+0x2ab/0x7f0 soft_offline_page_store+0x52/0x90 kernfs_fop_write_iter+0x12c/0x1d0 vfs_write+0x380/0x540 ksys_write+0x64/0xe0 do_syscall_64+0xb9/0x1d0 entry_SYSCALL_64_after_hwframe+0x77/0x7f RIP: 0033:0x7f5b3a514887 RSP: 002b:00007ffe138fce68 EFLAGS: 00000246 ORIG_RAX: 0000000000000001 RAX: ffffffffffffffda RBX: 000000000000000c RCX: 00007f5b3a514887 RDX: 000000000000000c RSI: 0000556ab809ee10 RDI: 0000000000000001 RBP: 0000556ab809ee10 R08: 00007f5b3a5d1460 R09: 000000007fffffff R10: 0000000000000000 R11: 0000000000000246 R12: 000000000000000c R13: 00007f5b3a61b780 R14: 00007f5b3a617600 R15: 00007f5b3a616a00 It's because hugetlb folio is passed to __folio_undo_large_rmappable() unexpectedly. large_rmappable flag is imperceptibly set to hugetlb folio since commit f6a8dd9 ("hugetlb: convert alloc_buddy_hugetlb_folio to use a folio"). Then commit be9581e ("mm: fix crashes from deferred split racing folio migration") makes folio_migrate_mapping() call folio_undo_large_rmappable() triggering the bug. Fix this issue by clearing large_rmappable flag for hugetlb folios. They don't need that flag set anyway. Link: https://lkml.kernel.org/r/[email protected] Fixes: f6a8dd9 ("hugetlb: convert alloc_buddy_hugetlb_folio to use a folio") Fixes: be9581e ("mm: fix crashes from deferred split racing folio migration") Signed-off-by: Miaohe Lin <[email protected]> Cc: Hugh Dickins <[email protected]> Cc: Matthew Wilcox (Oracle) <[email protected]> Cc: Muchun Song <[email protected]> Cc: <[email protected]> Signed-off-by: Andrew Morton <[email protected]>
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Maybe with one of the next kernel policy format changes one could minimize the ebitmap serialization.
Currently each serialized ebitmap contains the mapsize (which could be included once in the policy header) and the hightbit (which can be computed from the highest node plus the mapsize).
For example the current Reference policy compiles to a 1.9M file with 6970 ebitmaps, so
6970 * 2 * 4Byte - 4Byte(~ 2.9%) can be saved.The text was updated successfully, but these errors were encountered: