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[BUG] I have got at least two crash report for RAID6 syndrome generation, no matter if it's AVX2 or SSE2, they all seems to have a similar calltrace with corrupted RAX: BUG: kernel NULL pointer dereference, address: 0000000000000000 #PF: supervisor read access in kernel mode #PF: error_code(0x0000) - not-present page PGD 0 P4D 0 Oops: 0000 [#1] PREEMPT SMP PTI Workqueue: btrfs-rmw rmw_rbio_work [btrfs] RIP: 0010:raid6_sse21_gen_syndrome+0x9e/0x130 [raid6_pq] RAX: 0000000000000000 RBX: 0000000000001000 RCX: ffffa0ff4cfa3248 RDX: 0000000000000000 RSI: ffffa0f74cfa3238 RDI: 0000000000000000 Call Trace: <TASK> rmw_rbio+0x5c8/0xa80 [btrfs] process_one_work+0x1c7/0x3d0 worker_thread+0x4d/0x380 kthread+0xf3/0x120 ret_from_fork+0x2c/0x50 </TASK> [CAUSE] The cause is not known. Recently I also hit this in AVX512 path, and that's even in v5.15 backport, which doesn't have any of my RAID56 rework. Furthermore according to the registers: RAX: 0000000000000000 RBX: 0000000000001000 RCX: ffffa0ff4cfa3248 The RAX register is showing the number of stripes (including PQ), which is not correct (0). But the remaining two registers are all sane. - RBX is the sectorsize For x86_64 it should always be 4K and matches the output. - RCX is the pointers array Which is from rbio->finish_pointers, and it looks like a sane kernel address. [WORKAROUND] For now, I can only add extra debug ASSERT()s before we call raid6 gen_syndrome() helper and hopes to catch the problem. The debug requires both CONFIG_BTRFS_DEBUG and CONFIG_BTRFS_ASSERT enabled. My current guess is some use-after-free, but every report is only having corrupted RAX but seemingly valid pointers doesn't make much sense. Signed-off-by: Qu Wenruo <wqu@suse.com> Reviewed-by: David Sterba <dsterba@suse.com> Signed-off-by: David Sterba <dsterba@suse.com>
Linux kernel
============
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