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([2620:10d:c090:500::5:c621]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-327daeebe16sm31845461a91.26.2025.09.08.12.20.43 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 08 Sep 2025 12:20:44 -0700 (PDT) Message-ID: Subject: Re: [PATCH bpf-next v2 1/2] bpf: Reject bpf_timer for PREEMPT_RT From: Eduard Zingerman To: Leon Hwang , bpf@vger.kernel.org Cc: ast@kernel.org, andrii@kernel.org, daniel@iogearbox.net, martin.lau@linux.dev, song@kernel.org, yonghong.song@linux.dev, kernel-patches-bot@fb.com Date: Mon, 08 Sep 2025 12:20:42 -0700 In-Reply-To: <20250908044025.77519-2-leon.hwang@linux.dev> References: <20250908044025.77519-1-leon.hwang@linux.dev> <20250908044025.77519-2-leon.hwang@linux.dev> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.56.2 (3.56.2-1.fc42) Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Mon, 2025-09-08 at 12:40 +0800, Leon Hwang wrote: > When enable CONFIG_PREEMPT_RT, the kernel will panic when run timer > selftests by './test_progs -t timer': >=20 > [ 35.955287] BUG: sleeping function called from invalid context at kern= el/locking/spinlock_rt.c:48 > [ 35.955312] in_atomic(): 1, irqs_disabled(): 1, non_block: 0, pid: 120= , name: test_progs > [ 35.955315] preempt_count: 1, expected: 0 > [ 35.955316] RCU nest depth: 0, expected: 0 > [ 35.955317] 2 locks held by test_progs/120: > [ 35.955319] #0: ffffffff8f1c3720 (rcu_read_lock_trace){....}-{0:0}, a= t: bpf_prog_test_run_syscall+0xc9/0x240 > [ 35.955358] #1: ffff9155fbd331c8 ((&c->lock)){+.+.}-{3:3}, at: ___sla= b_alloc+0xb0/0xd20 > [ 35.955388] irq event stamp: 100 > [ 35.955389] hardirqs last enabled at (99): [] do_sy= scall_64+0x30/0x2d0 > [ 35.955414] hardirqs last disabled at (100): [] __bp= f_async_init+0xca/0x310 > [ 35.955428] softirqs last enabled at (0): [] copy_p= rocess+0x9db/0x2000 > [ 35.955449] softirqs last disabled at (0): [<0000000000000000>] 0x0 > [ 35.955482] CPU: 1 UID: 0 PID: 120 Comm: test_progs Tainted: G = OE 6.17.0-rc1-gc5f5af560d8a #30 PREEMPT_{RT,(full)} > [ 35.955487] Tainted: [O]=3DOOT_MODULE, [E]=3DUNSIGNED_MODULE > [ 35.955488] Hardware name: QEMU Ubuntu 24.04 PC (i440FX + PIIX, 1996),= BIOS 1.16.3-debian-1.16.3-2 04/01/2014 > [ 35.955491] Call Trace: > [ 35.955493] > [ 35.955499] dump_stack_lvl+0x73/0xb0 > [ 35.955514] dump_stack+0x14/0x20 > [ 35.955518] __might_resched+0x167/0x230 > [ 35.955537] rt_spin_lock+0x66/0x180 > [ 35.955543] ? ___slab_alloc+0xb0/0xd20 > [ 35.955549] ? bpf_map_kmalloc_node+0x7c/0x200 > [ 35.955560] ___slab_alloc+0xb0/0xd20 > [ 35.955575] ? __lock_acquire+0x43d/0x2590 > [ 35.955601] __kmalloc_node_noprof+0x10b/0x410 > [ 35.955605] ? __kmalloc_node_noprof+0x10b/0x410 > [ 35.955607] ? bpf_map_kmalloc_node+0x7c/0x200 > [ 35.955616] bpf_map_kmalloc_node+0x7c/0x200 > [ 35.955624] __bpf_async_init+0xf8/0x310 The error is reported because of the kmalloc call in the __bpf_async_init, = right? Instead of disabling timers for PREEMPT_RT, would it be possible to switch implementation to use kernel/bpf/memalloc.c:bpf_mem_alloc() instead? > [ 35.955633] bpf_timer_init+0x37/0x40 > [ 35.955637] bpf_prog_2287350dd5909839_start_cb+0x5d/0x91 > [ 35.955642] bpf_prog_0d54653d8a74e954_start_timer+0x65/0x8a > [ 35.955650] bpf_prog_test_run_syscall+0x111/0x240 > [ 35.955660] __sys_bpf+0x81c/0x2ab0 > [ 35.955665] ? __might_fault+0x47/0x90 > [ 35.955700] __x64_sys_bpf+0x1e/0x30 > [ 35.955703] x64_sys_call+0x171d/0x20d0 > [ 35.955715] do_syscall_64+0x6a/0x2d0 > [ 35.955722] entry_SYSCALL_64_after_hwframe+0x76/0x7e > [ 35.955728] RIP: 0033:0x7fee4261225d > [ 35.955734] Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 90 f3 0f 1e fa 4= 8 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <= 48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d 8b bb 0d 00 f7 d8 64 89 01 48 > [ 35.955736] RSP: 002b:00007fee424e5bd8 EFLAGS: 00000202 ORIG_RAX: 0000= 000000000141 > [ 35.955742] RAX: ffffffffffffffda RBX: 00007fee424e6cdc RCX: 00007fee4= 261225d > [ 35.955744] RDX: 0000000000000050 RSI: 00007fee424e5c20 RDI: 000000000= 000000a > [ 35.955745] RBP: 00007fee424e5bf0 R08: 0000000000000003 R09: 00007fee4= 24e5c20 > [ 35.955747] R10: 00007fffc266f910 R11: 0000000000000202 R12: 00007fee4= 24e66c0 > [ 35.955748] R13: ffffffffffffff08 R14: 0000000000000016 R15: 00007fffc= 266f650 > [ 35.955766] [...]