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b=tNq2tg7+q1RV93nSwDuwnuJqZ7uvrDZMpH5zJhkkacbZhStZ9RfwnaWcTiLVrdrC3 85zafAwMmXpd0qLy6CNgCClH4pM1Ex0nA8iJV+YRsJCqE9mDjqmgBTxerr3VofuhN1 2AsPoOf/fDT3XHDVsk5XYX1Yhvg44scna6PQ98awwipVCLzsjdyLhBl9cHOjzD0UGu 85iKx0RgLD9d28hDsOCSE3eoAqmOoFvpqscuuUlQu3AewrgsSJZA4H2XG3v9by67hz rWwk3rENIRtR9m+pYc4Sxi+sSx5hljkx15KDVbVq48bR387/9fow/5GdvkQcRRyNfH DcWzvQYmgYeAg== Date: Wed, 13 Nov 2024 08:53:09 +0900 From: Masami Hiramatsu (Google) To: Andrii Nakryiko Cc: Suren Baghdasaryan , Masami Hiramatsu , Andrii Nakryiko , linux-trace-kernel@vger.kernel.org, linux-mm@kvack.org, akpm@linux-foundation.org, peterz@infradead.org, oleg@redhat.com, rostedt@goodmis.org, bpf@vger.kernel.org, linux-kernel@vger.kernel.org, jolsa@kernel.org, paulmck@kernel.org, willy@infradead.org, mjguzik@gmail.com, brauner@kernel.org, jannh@google.com, mhocko@kernel.org, vbabka@suse.cz, shakeel.butt@linux.dev, hannes@cmpxchg.org, Liam.Howlett@oracle.com, lorenzo.stoakes@oracle.com, david@redhat.com, arnd@arndb.de, richard.weiyang@gmail.com, zhangpeng.00@bytedance.com, linmiaohe@huawei.com, viro@zeniv.linux.org.uk, hca@linux.ibm.com Subject: Re: [PATCH v4 tip/perf/core 4/4] uprobes: add speculative lockless VMA-to-inode-to-uprobe resolution Message-Id: <20241113085309.e3752f5c33f86106fcb81180@kernel.org> In-Reply-To: References: <20241028010818.2487581-1-andrii@kernel.org> <20241028010818.2487581-5-andrii@kernel.org> <20241112092816.cf5b0aa1ef10f50ce872892f@kernel.org> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 672401C000C X-Stat-Signature: cu1uacbftt9a8f1sqc9omf8qhyriw7se X-Rspam-User: X-HE-Tag: 1731455544-335080 X-HE-Meta: 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 5L9tpIwl 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, 12 Nov 2024 10:09:58 -0800 Andrii Nakryiko wrote: > On Mon, Nov 11, 2024 at 5:05 PM Suren Baghdasaryan wrote: > > > > On Mon, Nov 11, 2024 at 4:28 PM Masami Hiramatsu wrote: > > > > > > On Sun, 27 Oct 2024 18:08:18 -0700 > > > Andrii Nakryiko wrote: > > > > > > > Given filp_cachep is marked SLAB_TYPESAFE_BY_RCU (and FMODE_BACKING > > > > files, a special case, now goes through RCU-delated freeing), we can > > > > safely access vma->vm_file->f_inode field locklessly under just > > > > rcu_read_lock() protection, which enables looking up uprobe from > > > > uprobes_tree completely locklessly and speculatively without the need to > > > > acquire mmap_lock for reads. In most cases, anyway, assuming that there > > > > are no parallel mm and/or VMA modifications. The underlying struct > > > > file's memory won't go away from under us (even if struct file can be > > > > reused in the meantime). > > > > > > > > We rely on newly added mmap_lock_speculation_{begin,end}() helpers to > > > > validate that mm_struct stays intact for entire duration of this > > > > speculation. If not, we fall back to mmap_lock-protected lookup. > > > > The speculative logic is written in such a way that it will safely > > > > handle any garbage values that might be read from vma or file structs. > > > > > > > > Benchmarking results speak for themselves. > > > > > > > > BEFORE (latest tip/perf/core) > > > > ============================= > > > > uprobe-nop ( 1 cpus): 3.384 ± 0.004M/s ( 3.384M/s/cpu) > > > > uprobe-nop ( 2 cpus): 5.456 ± 0.005M/s ( 2.728M/s/cpu) > > > > uprobe-nop ( 3 cpus): 7.863 ± 0.015M/s ( 2.621M/s/cpu) > > > > uprobe-nop ( 4 cpus): 9.442 ± 0.008M/s ( 2.360M/s/cpu) > > > > uprobe-nop ( 5 cpus): 11.036 ± 0.013M/s ( 2.207M/s/cpu) > > > > uprobe-nop ( 6 cpus): 10.884 ± 0.019M/s ( 1.814M/s/cpu) > > > > uprobe-nop ( 7 cpus): 7.897 ± 0.145M/s ( 1.128M/s/cpu) > > > > uprobe-nop ( 8 cpus): 10.021 ± 0.128M/s ( 1.253M/s/cpu) > > > > uprobe-nop (10 cpus): 9.932 ± 0.170M/s ( 0.993M/s/cpu) > > > > uprobe-nop (12 cpus): 8.369 ± 0.056M/s ( 0.697M/s/cpu) > > > > uprobe-nop (14 cpus): 8.678 ± 0.017M/s ( 0.620M/s/cpu) > > > > uprobe-nop (16 cpus): 7.392 ± 0.003M/s ( 0.462M/s/cpu) > > > > uprobe-nop (24 cpus): 5.326 ± 0.178M/s ( 0.222M/s/cpu) > > > > uprobe-nop (32 cpus): 5.426 ± 0.059M/s ( 0.170M/s/cpu) > > > > uprobe-nop (40 cpus): 5.262 ± 0.070M/s ( 0.132M/s/cpu) > > > > uprobe-nop (48 cpus): 6.121 ± 0.010M/s ( 0.128M/s/cpu) > > > > uprobe-nop (56 cpus): 6.252 ± 0.035M/s ( 0.112M/s/cpu) > > > > uprobe-nop (64 cpus): 7.644 ± 0.023M/s ( 0.119M/s/cpu) > > > > uprobe-nop (72 cpus): 7.781 ± 0.001M/s ( 0.108M/s/cpu) > > > > uprobe-nop (80 cpus): 8.992 ± 0.048M/s ( 0.112M/s/cpu) > > > > > > > > AFTER > > > > ===== > > > > uprobe-nop ( 1 cpus): 3.534 ± 0.033M/s ( 3.534M/s/cpu) > > > > uprobe-nop ( 2 cpus): 6.701 ± 0.007M/s ( 3.351M/s/cpu) > > > > uprobe-nop ( 3 cpus): 10.031 ± 0.007M/s ( 3.344M/s/cpu) > > > > uprobe-nop ( 4 cpus): 13.003 ± 0.012M/s ( 3.251M/s/cpu) > > > > uprobe-nop ( 5 cpus): 16.274 ± 0.006M/s ( 3.255M/s/cpu) > > > > uprobe-nop ( 6 cpus): 19.563 ± 0.024M/s ( 3.261M/s/cpu) > > > > uprobe-nop ( 7 cpus): 22.696 ± 0.054M/s ( 3.242M/s/cpu) > > > > uprobe-nop ( 8 cpus): 24.534 ± 0.010M/s ( 3.067M/s/cpu) > > > > uprobe-nop (10 cpus): 30.475 ± 0.117M/s ( 3.047M/s/cpu) > > > > uprobe-nop (12 cpus): 33.371 ± 0.017M/s ( 2.781M/s/cpu) > > > > uprobe-nop (14 cpus): 38.864 ± 0.004M/s ( 2.776M/s/cpu) > > > > uprobe-nop (16 cpus): 41.476 ± 0.020M/s ( 2.592M/s/cpu) > > > > uprobe-nop (24 cpus): 64.696 ± 0.021M/s ( 2.696M/s/cpu) > > > > uprobe-nop (32 cpus): 85.054 ± 0.027M/s ( 2.658M/s/cpu) > > > > uprobe-nop (40 cpus): 101.979 ± 0.032M/s ( 2.549M/s/cpu) > > > > uprobe-nop (48 cpus): 110.518 ± 0.056M/s ( 2.302M/s/cpu) > > > > uprobe-nop (56 cpus): 117.737 ± 0.020M/s ( 2.102M/s/cpu) > > > > uprobe-nop (64 cpus): 124.613 ± 0.079M/s ( 1.947M/s/cpu) > > > > uprobe-nop (72 cpus): 133.239 ± 0.032M/s ( 1.851M/s/cpu) > > > > uprobe-nop (80 cpus): 142.037 ± 0.138M/s ( 1.775M/s/cpu) > > > > > > > > Previously total throughput was maxing out at 11mln/s, and gradually > > > > declining past 8 cores. With this change, it now keeps growing with each > > > > added CPU, reaching 142mln/s at 80 CPUs (this was measured on a 80-core > > > > Intel(R) Xeon(R) Gold 6138 CPU @ 2.00GHz). > > > > > > > > > > Looks good to me, except one question below. > > > > > > > Reviewed-by: Oleg Nesterov > > > > Suggested-by: Matthew Wilcox > > > > Suggested-by: Peter Zijlstra > > > > Signed-off-by: Andrii Nakryiko > > > > --- > > > > kernel/events/uprobes.c | 45 +++++++++++++++++++++++++++++++++++++++++ > > > > 1 file changed, 45 insertions(+) > > > > > > > > diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c > > > > index 290c445768fa..efcd62f7051d 100644 > > > > --- a/kernel/events/uprobes.c > > > > +++ b/kernel/events/uprobes.c > > > > @@ -2074,6 +2074,47 @@ static int is_trap_at_addr(struct mm_struct *mm, unsigned long vaddr) > > > > return is_trap_insn(&opcode); > > > > } > > > > > > > > +static struct uprobe *find_active_uprobe_speculative(unsigned long bp_vaddr) > > > > +{ > > > > + struct mm_struct *mm = current->mm; > > > > + struct uprobe *uprobe = NULL; > > > > + struct vm_area_struct *vma; > > > > + struct file *vm_file; > > > > + loff_t offset; > > > > + unsigned int seq; > > > > + > > > > + guard(rcu)(); > > > > + > > > > + if (!mmap_lock_speculation_begin(mm, &seq)) > > > > + return NULL; > > > > + > > > > + vma = vma_lookup(mm, bp_vaddr); > > > > + if (!vma) > > > > + return NULL; > > > > + > > > > + /* > > > > + * vm_file memory can be reused for another instance of struct file, > > > > + * but can't be freed from under us, so it's safe to read fields from > > > > + * it, even if the values are some garbage values; ultimately > > > > + * find_uprobe_rcu() + mmap_lock_speculation_end() check will ensure > > > > + * that whatever we speculatively found is correct > > > > > > If vm_file is a garbage value, may `vm_file->f_inode` access be dangerous? > > > > > > > + */ > > > > + vm_file = READ_ONCE(vma->vm_file); > > > > + if (!vm_file) > > > > + return NULL; > > > > + > > > > + offset = (loff_t)(vma->vm_pgoff << PAGE_SHIFT) + (bp_vaddr - vma->vm_start); > > > > + uprobe = find_uprobe_rcu(vm_file->f_inode, offset); > > > ^^^^ Here > > > > > > if it only stores vm_file or NULL, there's no problem. > > > > IIRC correctly, vma->vm_file is RCU-safe and we are in the read RCU > > section, so it should not contain a garbage value. > > Correct. vm_file itself can be either TYPESAFE_BY_RCU for normal > files, or properly RCU protected for FMODE_BACKING ones. Either way, > there is some correct struct file pointed to, and so all this is valid > and won't dereference invalid memory. OK, thanks for confirmation! This looks good to me. Acked-by: Masami Hiramatsu (Google) Thank you, > > > > > > > > > Thank you, > > > > > > > + if (!uprobe) > > > > + return NULL; > > > > + > > > > + /* now double check that nothing about MM changed */ > > > > + if (!mmap_lock_speculation_end(mm, seq)) > > > > + return NULL; > > > > + > > > > + return uprobe; > > > > +} > > > > + > > > > /* assumes being inside RCU protected region */ > > > > static struct uprobe *find_active_uprobe_rcu(unsigned long bp_vaddr, int *is_swbp) > > > > { > > > > @@ -2081,6 +2122,10 @@ static struct uprobe *find_active_uprobe_rcu(unsigned long bp_vaddr, int *is_swb > > > > struct uprobe *uprobe = NULL; > > > > struct vm_area_struct *vma; > > > > > > > > + uprobe = find_active_uprobe_speculative(bp_vaddr); > > > > + if (uprobe) > > > > + return uprobe; > > > > + > > > > mmap_read_lock(mm); > > > > vma = vma_lookup(mm, bp_vaddr); > > > > if (vma) { > > > > -- > > > > 2.43.5 > > > > > > > > > > > > > -- > > > Masami Hiramatsu (Google) -- Masami Hiramatsu (Google)