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Date: Sat, 29 Aug 2020 15:13:23 -0700 From: Yonghong Song <yhs@...com> To: Alexei Starovoitov <alexei.starovoitov@...il.com>, <davem@...emloft.net> CC: <daniel@...earbox.net>, <josef@...icpanda.com>, <bpoirier@...e.com>, <akpm@...ux-foundation.org>, <hannes@...xchg.org>, <netdev@...r.kernel.org>, <bpf@...r.kernel.org>, <kernel-team@...com> Subject: Re: [PATCH v3 bpf-next 5/5] selftests/bpf: Add sleepable tests On 8/27/20 3:01 PM, Alexei Starovoitov wrote: > From: Alexei Starovoitov <ast@...nel.org> > > Modify few tests to sanity test sleepable bpf functionality. > > Running 'bench trig-fentry-sleep' vs 'bench trig-fentry' and 'perf report': > sleepable with SRCU: > 3.86% bench [k] __srcu_read_unlock > 3.22% bench [k] __srcu_read_lock > 0.92% bench [k] bpf_prog_740d4210cdcd99a3_bench_trigger_fentry_sleep > 0.50% bench [k] bpf_trampoline_10297 > 0.26% bench [k] __bpf_prog_exit_sleepable > 0.21% bench [k] __bpf_prog_enter_sleepable > > sleepable with RCU_TRACE: > 0.79% bench [k] bpf_prog_740d4210cdcd99a3_bench_trigger_fentry_sleep > 0.72% bench [k] bpf_trampoline_10381 > 0.31% bench [k] __bpf_prog_exit_sleepable > 0.29% bench [k] __bpf_prog_enter_sleepable > > non-sleepable with RCU: > 0.88% bench [k] bpf_prog_740d4210cdcd99a3_bench_trigger_fentry > 0.84% bench [k] bpf_trampoline_10297 > 0.13% bench [k] __bpf_prog_enter > 0.12% bench [k] __bpf_prog_exit > > Signed-off-by: Alexei Starovoitov <ast@...nel.org> > Acked-by: KP Singh <kpsingh@...gle.com> > --- > tools/testing/selftests/bpf/bench.c | 2 + > .../selftests/bpf/benchs/bench_trigger.c | 17 +++++ > .../selftests/bpf/prog_tests/test_lsm.c | 9 +++ > tools/testing/selftests/bpf/progs/lsm.c | 66 ++++++++++++++++++- > .../selftests/bpf/progs/trigger_bench.c | 7 ++ > 5 files changed, 99 insertions(+), 2 deletions(-) > [...] > diff --git a/tools/testing/selftests/bpf/progs/lsm.c b/tools/testing/selftests/bpf/progs/lsm.c > index b4598d4bc4f7..49fa6ca99755 100644 > --- a/tools/testing/selftests/bpf/progs/lsm.c > +++ b/tools/testing/selftests/bpf/progs/lsm.c > @@ -9,16 +9,41 @@ > #include <bpf/bpf_tracing.h> > #include <errno.h> > > +struct { > + __uint(type, BPF_MAP_TYPE_ARRAY); > + __uint(max_entries, 1); > + __type(key, __u32); > + __type(value, __u64); > +} array SEC(".maps"); > + > +struct { > + __uint(type, BPF_MAP_TYPE_HASH); > + __uint(max_entries, 1); > + __type(key, __u32); > + __type(value, __u64); > +} hash SEC(".maps"); > + > +struct { > + __uint(type, BPF_MAP_TYPE_LRU_HASH); > + __uint(max_entries, 1); > + __type(key, __u32); > + __type(value, __u64); > +} lru_hash SEC(".maps"); > + > char _license[] SEC("license") = "GPL"; > > int monitored_pid = 0; > int mprotect_count = 0; > int bprm_count = 0; > > -SEC("lsm/file_mprotect") > +SEC("lsm.s/file_mprotect") When running selftest, I hit the following kernel warning: [ 250.871267] ============================================ [ 250.871902] WARNING: possible recursive locking detected [ 250.872561] 5.9.0-rc1+ #830 Not tainted [ 250.873166] -------------------------------------------- [ 250.873991] true/2053 is trying to acquire lock: [ 250.874715] ffff8fc1f9cd2068 (&mm->mmap_lock#2){++++}-{3:3}, at: __might_fault+0x3e/0x90 [ 250.875943] [ 250.875943] but task is already holding lock: [ 250.876688] ffff8fc1f9cd2068 (&mm->mmap_lock#2){++++}-{3:3}, at: do_mprotect_pkey+0xb5/0x2f0 [ 250.877978] [ 250.877978] other info that might help us debug this: [ 250.878797] Possible unsafe locking scenario: [ 250.878797] [ 250.879708] CPU0 [ 250.880095] ---- [ 250.880482] lock(&mm->mmap_lock#2); [ 250.881063] lock(&mm->mmap_lock#2); [ 250.881645] [ 250.881645] *** DEADLOCK *** [ 250.881645] [ 250.882559] May be due to missing lock nesting notation [ 250.882559] [ 250.883613] 2 locks held by true/2053: [ 250.884194] #0: ffff8fc1f9cd2068 (&mm->mmap_lock#2){++++}-{3:3}, at: do_mprotect_pkey+0xb5/0x2f0 [ 250.885558] #1: ffffffffbc47b8a0 (rcu_read_lock_trace){....}-{0:0}, at: __bpf_prog_enter_sleepable+0x0/0x40 [ 250.887062] [ 250.887062] stack backtrace: [ 250.887583] CPU: 1 PID: 2053 Comm: true Not tainted 5.9.0-rc1+ #830 [ 250.888546] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.9.3-1.el7.centos 04/01/2014 [ 250.889896] Call Trace: [ 250.890222] dump_stack+0x78/0xa0 [ 250.890644] __lock_acquire.cold.74+0x209/0x2e3 [ 250.891350] lock_acquire+0xba/0x380 [ 250.891919] ? __might_fault+0x3e/0x90 [ 250.892510] ? __lock_acquire+0x639/0x20c0 [ 250.893150] __might_fault+0x68/0x90 [ 250.893717] ? __might_fault+0x3e/0x90 [ 250.894325] _copy_from_user+0x1e/0xa0 [ 250.894946] bpf_copy_from_user+0x22/0x50 [ 250.895581] bpf_prog_3717002769f30998_test_int_hook+0x76/0x60c [ 250.896446] ? __bpf_prog_enter_sleepable+0x3c/0x40 [ 250.897207] ? __bpf_prog_exit+0xa0/0xa0 [ 250.897819] bpf_trampoline_18669+0x29/0x1000 [ 250.898476] bpf_lsm_file_mprotect+0x5/0x10 [ 250.899133] security_file_mprotect+0x32/0x50 [ 250.899816] do_mprotect_pkey+0x18a/0x2f0 [ 250.900472] __x64_sys_mprotect+0x1b/0x20 [ 250.901107] do_syscall_64+0x33/0x40 [ 250.901670] entry_SYSCALL_64_after_hwframe+0x44/0xa9 [ 250.902450] RIP: 0033:0x7fd95c141ef7 [ 250.903014] Code: ff 66 90 b8 0b 00 00 00 0f 05 48 3d 01 f0 ff ff 73 01 c3 48 8d 0d 21 c2 2 0 00 f7 d8 89 01 48 83 c8 ff c3 b8 0a 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8d 0d 01 c2 20 00 f7 d8 89 01 48 83 [ 250.905732] RSP: 002b:00007ffd4c291fe8 EFLAGS: 00000246 ORIG_RAX: 000000000000000a [ 250.906773] RAX: ffffffffffffffda RBX: 0000000000000005 RCX: 00007fd95c141ef7 [ 250.907866] RDX: 0000000000000000 RSI: 00000000001ff000 RDI: 00007fd95bf20000 [ 250.908906] RBP: 00007ffd4c292320 R08: 0000000000000000 R09: 0000000000000000 [ 250.909915] R10: 00007ffd4c291ff0 R11: 0000000000000246 R12: 00007fd95c341000 [ 250.910919] R13: 00007ffd4c292408 R14: 0000000000000002 R15: 0000000000000801 Could this be an real issue here? do_mprotect_pkey() gets a lock of current->mm->mmap_lock before calling security_file_mprotect(bpf_lsm_file_mprotect). Later on, when do _copy_to_user(), page fault may happen and current->mm->mmap_lock might be acquired again and may have a deadlock here? > int BPF_PROG(test_int_hook, struct vm_area_struct *vma, > unsigned long reqprot, unsigned long prot, int ret) > { > + char args[64]; > + __u32 key = 0; > + __u64 *value; > + > if (ret != 0) > return ret; > > @@ -28,6 +53,18 @@ int BPF_PROG(test_int_hook, struct vm_area_struct *vma, > is_stack = (vma->vm_start <= vma->vm_mm->start_stack && > vma->vm_end >= vma->vm_mm->start_stack); > > + bpf_copy_from_user(args, sizeof(args), (void *)vma->vm_mm->arg_start); > + > + value = bpf_map_lookup_elem(&array, &key); > + if (value) > + *value = 0; > + value = bpf_map_lookup_elem(&hash, &key); > + if (value) > + *value = 0; > + value = bpf_map_lookup_elem(&lru_hash, &key); > + if (value) > + *value = 0; > + > if (is_stack && monitored_pid == pid) { > mprotect_count++; > ret = -EPERM; > @@ -36,7 +73,7 @@ int BPF_PROG(test_int_hook, struct vm_area_struct *vma, > return ret; > } > [...]
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