Messages in this thread | | | Subject | Re: [PATCH v2] x86/cpu: replacing the open-coded shift with BIT(x) | From | cuigaosheng <> | Date | Tue, 1 Nov 2022 21:37:02 +0800 |
| |
> Others might feel differently and that's fine, but I always found the > BIT() thing so much less clear than doing 1<<n, which is not only a > pattern that I recognize as builtin to my brain, but also provides a > direct description of what's happening, "shift a 1 over n times", > leaving no off-by-one ambiguity about it. If anything I'd like to see > the BIT() macro expanded throughout and then removed entirely. > > Probably just me though. You can safely ignore my opinion.
Thanks for taking time to review the patch, I submit the patch to remove the UBSAN warning, even it's not a bug, for example, when I am testing the kernel, I get some logs as follows, maybe it's better to avoid this?
> [ 0.951719][ T0] > ================================================================================ > 215 [ 0.953146][ T0] UBSAN: shift-out-of-bounds in mm/shmem.c:3749:18 > 216 [ 0.953863][ T0] left shift of 1 by 31 places cannot be > represented in type 'int' 217 [ 0.955067][ T0] CPU: 0 PID: 0 Comm: > swapper/0 Not tainted 6.1.0-rc2-00062-ga970174d7a10 #5 218 [ > 0.956400][ T0] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), > BIOS rel-1.13.0-48-gd9c812dda519-prebuilt.qemu.org 04/01/2014 219 [ > 0.958278][ T0] Call Trace: 220 [ 0.958777][ T0] <TASK> 221 [ > 0.959224][ T0] dump_stack_lvl+0x8d/0xcf 222 [ 0.959922][ T0] > ubsan_epilogue+0xa/0x44 223 [ 0.960599][ T0] > __ubsan_handle_shift_out_of_bounds+0x1e7/0x208 224 [ 0.961575][ T0] ? > __kmem_cache_alloc_node+0x167/0x290 225 [ 0.962434][ T0] ? > shmem_fill_super+0x2e/0x2e0 226 [ 0.963187][ T0] ? > rcu_read_lock_held_common+0x9/0x40 227 [ 0.963857][ T0] ? > shmem_alloc_hugefolio+0x110/0x110 228 [ 0.963857][ T0] ? > shmem_fill_super+0x2cc/0x2e0 229 [ 0.963857][ T0] > shmem_fill_super+0x2cc/0x2e0 230 [ 0.963857][ T0] > vfs_get_super+0x78/0x160 231 [ 0.963857][ T0] vfs_get_tree+0x28/0x100 > 232 [ 0.963857][ T0] fc_mount+0x12/0x60 233 [ 0.963857][ T0] > vfs_kern_mount.part.38+0xa5/0xc0 234 [ 0.963857][ T0] > kern_mount+0x2e/0x60 235 [ 0.963857][ T0] shmem_init+0x63/0xef 236 [ > 0.963857][ T0] mnt_init+0x159/0x2e0 237 [ 0.963857][ T0] ? > trace_init_perf_perm_irq_work_exit+0xe/0xe 238 [ 0.963857][ T0] > vfs_caches_init+0xd4/0xde 239 [ 0.963857][ T0] > start_kernel+0x837/0x8a4 240 [ 0.963857][ T0] > secondary_startup_64_no_verify+0xce/0xdb 241 [ 0.963857][ T0] </TASK> > 242 [ 0.963860][ T0] > ================================================================================ > 243 [ 0.965288][ T0] Kernel panic - not syncing: panic_on_warn set ... > 244 [ 0.966299][ T0] CPU: 0 PID: 0 Comm: swapper/0 Not tainted > 6.1.0-rc2-00062-ga970174d7a10 #5 245 [ 0.967645][ T0] Hardware name: > QEMU Standard PC (i440FX + PIIX, 1996), BIOS > rel-1.13.0-48-gd9c812dda519-prebuilt.qemu.org 04/01/2014 246 [ > 0.969548][ T0] Call Trace: 247 [ 0.970050][ T0] <TASK> 248 [ > 0.970499][ T0] dump_stack_lvl+0x8d/0xcf 249 [ 0.971195][ T0] > panic+0x182/0x387 250 [ 0.971797][ T0] ? ubsan_epilogue+0x33/0x44 251 > [ 0.972539][ T0] ubsan_epilogue+0x3f/0x44 252 [ 0.973237][ T0] > __ubsan_handle_shift_out_of_bounds+0x1e7/0x208 253 [ 0.973857][ T0] ? > __kmem_cache_alloc_node+0x167/0x290 254 [ 0.973857][ T0] ? > shmem_fill_super+0x2e/0x2e0 255 [ 0.973857][ T0] ? > rcu_read_lock_held_common+0x9/0x40 256 [ 0.973857][ T0] ? > shmem_alloc_hugefolio+0x110/0x110 257 [ 0.973857][ T0] ? > shmem_fill_super+0x2cc/0x2e0 258 [ 0.973857][ T0] > shmem_fill_super+0x2cc/0x2e0 259 [ 0.973857][ T0] > vfs_get_super+0x78/0x160 260 [ 0.973857][ T0] vfs_get_tree+0x28/0x100 > 261 [ 0.973857][ T0] fc_mount+0x12/0x60 262 [ 0.973857][ T0] > vfs_kern_mount.part.38+0xa5/0xc0 263 [ 0.973857][ T0] > kern_mount+0x2e/0x60 264 [ 0.973857][ T0] shmem_init+0x63/0xef 265 [ > 0.973857][ T0] mnt_init+0x159/0x2e0 266 [ 0.973857][ T0] ? > trace_init_perf_perm_irq_work_exit+0xe/0xe 267 [ 0.973857][ T0] > vfs_caches_init+0xd4/0xde 268 [ 0.973857][ T0] > start_kernel+0x837/0x8a4 269 [ 0.973857][ T0] > secondary_startup_64_no_verify+0xce/0xdb 270 [ 0.973857][ T0] </TASK> > 271 [ 0.973857][ T0] Rebooting in 86400 seconds..
On 2022/11/1 19:34, Jason A. Donenfeld wrote: > Others might feel differently and that's fine, but I always found the > BIT() thing so much less clear than doing 1<<n, which is not only a > pattern that I recognize as builtin to my brain, but also provides a > direct description of what's happening, "shift a 1 over n times", > leaving no off-by-one ambiguity about it. If anything I'd like to see > the BIT() macro expanded throughout and then removed entirely. > > Probably just me though. You can safely ignore my opinion:).
| |