Messages in this thread Patch in this message | | | From | Like Xu <> | Subject | [PATCH v3 2/2] perf/x86/lbr: Move cpuc->lbr_xsave allocation out of sleeping region | Date | Tue, 18 May 2021 22:26:12 +0800 |
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If the kernel is compiled with the CONFIG_LOCKDEP option, the conditional might_sleep_if() deep in kmem_cache_alloc() will generate the following trace, and potentially cause a deadlock when another LBR event is added:
[ 243.115549] BUG: sleeping function called from invalid context at include/linux/sched/mm.h:196 [ 243.117576] in_atomic(): 1, irqs_disabled(): 1, non_block: 0, pid: 839, name: perf [ 243.119326] INFO: lockdep is turned off. [ 243.120249] irq event stamp: 0 [ 243.120967] hardirqs last enabled at (0): [<0000000000000000>] 0x0 [ 243.122415] hardirqs last disabled at (0): [<ffffffff810d9bf5>] copy_process+0xa45/0x1dc0 [ 243.124302] softirqs last enabled at (0): [<ffffffff810d9bf5>] copy_process+0xa45/0x1dc0 [ 243.126255] softirqs last disabled at (0): [<0000000000000000>] 0x0 [ 243.128119] CPU: 0 PID: 839 Comm: perf Not tainted 5.11.0-rc4-guest+ #8 [ 243.129654] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 0.0.0 02/06/2015 [ 243.131520] Call Trace: [ 243.132112] dump_stack+0x8d/0xb5 [ 243.132896] ___might_sleep.cold.106+0xb3/0xc3 [ 243.133984] slab_pre_alloc_hook.constprop.85+0x96/0xd0 [ 243.135208] ? intel_pmu_lbr_add+0x152/0x170 [ 243.136207] kmem_cache_alloc+0x36/0x250 [ 243.137126] intel_pmu_lbr_add+0x152/0x170 [ 243.138088] x86_pmu_add+0x83/0xd0 [ 243.138889] ? lock_acquire+0x158/0x350 [ 243.139791] ? lock_acquire+0x158/0x350 [ 243.140694] ? lock_acquire+0x158/0x350 [ 243.141625] ? lock_acquired+0x1e3/0x360 [ 243.142544] ? lock_release+0x1bf/0x340 [ 243.143726] ? trace_hardirqs_on+0x1a/0xd0 [ 243.144823] ? lock_acquired+0x1e3/0x360 [ 243.145742] ? lock_release+0x1bf/0x340 [ 243.147107] ? __slab_free+0x49/0x540 [ 243.147966] ? trace_hardirqs_on+0x1a/0xd0 [ 243.148924] event_sched_in.isra.129+0xf8/0x2a0 [ 243.149989] merge_sched_in+0x261/0x3e0 [ 243.150889] ? trace_hardirqs_on+0x1a/0xd0 [ 243.151869] visit_groups_merge.constprop.135+0x130/0x4a0 [ 243.153122] ? sched_clock_cpu+0xc/0xb0 [ 243.154023] ctx_sched_in+0x101/0x210 [ 243.154884] ctx_resched+0x6f/0xc0 [ 243.155686] perf_event_exec+0x21e/0x2e0 [ 243.156641] begin_new_exec+0x5e5/0xbd0 [ 243.157540] load_elf_binary+0x6af/0x1770 [ 243.158478] ? __kernel_read+0x19d/0x2b0 [ 243.159977] ? lock_acquire+0x158/0x350 [ 243.160876] ? __kernel_read+0x19d/0x2b0 [ 243.161796] bprm_execve+0x3c8/0x840 [ 243.162638] do_execveat_common.isra.38+0x1a5/0x1c0 [ 243.163776] __x64_sys_execve+0x32/0x40 [ 243.164676] do_syscall_64+0x33/0x40 [ 243.165514] entry_SYSCALL_64_after_hwframe+0x44/0xa9 [ 243.166746] RIP: 0033:0x7f6180a26feb [ 243.167590] Code: Unable to access opcode bytes at RIP 0x7f6180a26fc1. [ 243.169097] RSP: 002b:00007ffc6558ce18 EFLAGS: 00000202 ORIG_RAX: 000000000000003b [ 243.170844] RAX: ffffffffffffffda RBX: 00007ffc65592d30 RCX: 00007f6180a26feb [ 243.172514] RDX: 000055657f408dc0 RSI: 00007ffc65592410 RDI: 00007ffc65592d30 [ 243.174162] RBP: 00007ffc6558ce80 R08: 00007ffc6558cde0 R09: 0000000000000000 [ 243.176042] R10: 0000000000000008 R11: 0000000000000202 R12: 00007ffc65592410 [ 243.177696] R13: 000055657f408dc0 R14: 0000000000000001 R15: 00007ffc65592410
One of the solution is to use GFP_ATOMIC, but it will make the code less reliable under memory pressue. Let's move the memory allocation out of the sleeping region and put it into the intel_pmu_hw_config(). The LBR xsave buffer is a per-CPU buffer, not a per-event buffer. This buffer is allocated once when initializing the first LBR event.
The disadvantage of this fix is that the cpuc->lbr_xsave memory will be allocated for each cpu like the legacy ds_buffer.
Fixes: c085fb8774 ("perf/x86/intel/lbr: Support XSAVES for arch LBR read") Tested-by: Kan Liang <kan.liang@linux.intel.com> Signed-off-by: Like Xu <like.xu@linux.intel.com> --- v2->v3 Changelog: - drop !precise_ip check; - go back to the original v1 form, which makes much more sense since now reserve and release are symmetric.
arch/x86/events/core.c | 6 ++++-- arch/x86/events/intel/lbr.c | 26 ++++++++++++++++++++------ arch/x86/events/perf_event.h | 6 ++++++ 3 files changed, 30 insertions(+), 8 deletions(-)
diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c index 8e509325c2c3..8f71dd72ef95 100644 --- a/arch/x86/events/core.c +++ b/arch/x86/events/core.c @@ -396,10 +396,12 @@ int x86_reserve_hardware(void) if (!atomic_inc_not_zero(&pmc_refcount)) { mutex_lock(&pmc_reserve_mutex); if (atomic_read(&pmc_refcount) == 0) { - if (!reserve_pmc_hardware()) + if (!reserve_pmc_hardware()) { err = -EBUSY; - else + } else { reserve_ds_buffers(); + reserve_lbr_buffers(); + } } if (!err) atomic_inc(&pmc_refcount); diff --git a/arch/x86/events/intel/lbr.c b/arch/x86/events/intel/lbr.c index 76dbab6ac9fb..4409d2cccfda 100644 --- a/arch/x86/events/intel/lbr.c +++ b/arch/x86/events/intel/lbr.c @@ -658,7 +658,6 @@ static inline bool branch_user_callstack(unsigned br_sel) void intel_pmu_lbr_add(struct perf_event *event) { - struct kmem_cache *kmem_cache = event->pmu->task_ctx_cache; struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events); if (!x86_pmu.lbr_nr) @@ -696,11 +695,6 @@ void intel_pmu_lbr_add(struct perf_event *event) perf_sched_cb_inc(event->ctx->pmu); if (!cpuc->lbr_users++ && !event->total_time_running) intel_pmu_lbr_reset(); - - if (static_cpu_has(X86_FEATURE_ARCH_LBR) && - kmem_cache && !cpuc->lbr_xsave && - (cpuc->lbr_users != cpuc->lbr_pebs_users)) - cpuc->lbr_xsave = kmem_cache_alloc(kmem_cache, GFP_KERNEL); } void release_lbr_buffers(void) @@ -722,6 +716,26 @@ void release_lbr_buffers(void) } } +void reserve_lbr_buffers(void) +{ + struct kmem_cache *kmem_cache; + struct cpu_hw_events *cpuc; + int cpu; + + if (!static_cpu_has(X86_FEATURE_ARCH_LBR)) + return; + + for_each_possible_cpu(cpu) { + cpuc = per_cpu_ptr(&cpu_hw_events, cpu); + kmem_cache = x86_get_pmu(cpu)->task_ctx_cache; + if (!kmem_cache || cpuc->lbr_xsave) + continue; + + cpuc->lbr_xsave = kmem_cache_alloc_node(kmem_cache, GFP_KERNEL, + cpu_to_node(cpu)); + } +} + void intel_pmu_lbr_del(struct perf_event *event) { struct cpu_hw_events *cpuc = this_cpu_ptr(&cpu_hw_events); diff --git a/arch/x86/events/perf_event.h b/arch/x86/events/perf_event.h index 27fa85e7d4fd..ad87cb36f7c8 100644 --- a/arch/x86/events/perf_event.h +++ b/arch/x86/events/perf_event.h @@ -1244,6 +1244,8 @@ void reserve_ds_buffers(void); void release_lbr_buffers(void); +void reserve_lbr_buffers(void); + extern struct event_constraint bts_constraint; extern struct event_constraint vlbr_constraint; @@ -1393,6 +1395,10 @@ static inline void release_lbr_buffers(void) { } +static inline void reserve_lbr_buffers(void) +{ +} + static inline int intel_pmu_init(void) { return 0; -- 2.31.1
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