| Message ID | 20241028010818.2487581-5-andrii@kernel.org (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | uprobes,mm: speculative lockless VMA-to-uprobe lookup | expand |
On Sun, 27 Oct 2024 18:08:18 -0700 Andrii Nakryiko <andrii@kernel.org> 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 <oleg@redhat.com> > Suggested-by: Matthew Wilcox <willy@infradead.org> > Suggested-by: Peter Zijlstra <peterz@infradead.org> > Signed-off-by: Andrii Nakryiko <andrii@kernel.org> > --- > 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. 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 >
On Mon, Nov 11, 2024 at 4:28 PM Masami Hiramatsu <mhiramat@kernel.org> wrote: > > On Sun, 27 Oct 2024 18:08:18 -0700 > Andrii Nakryiko <andrii@kernel.org> 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 <oleg@redhat.com> > > Suggested-by: Matthew Wilcox <willy@infradead.org> > > Suggested-by: Peter Zijlstra <peterz@infradead.org> > > Signed-off-by: Andrii Nakryiko <andrii@kernel.org> > > --- > > 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. > > 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) <mhiramat@kernel.org>
On Mon, Nov 11, 2024 at 5:05 PM Suren Baghdasaryan <surenb@google.com> wrote: > > On Mon, Nov 11, 2024 at 4:28 PM Masami Hiramatsu <mhiramat@kernel.org> wrote: > > > > On Sun, 27 Oct 2024 18:08:18 -0700 > > Andrii Nakryiko <andrii@kernel.org> 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 <oleg@redhat.com> > > > Suggested-by: Matthew Wilcox <willy@infradead.org> > > > Suggested-by: Peter Zijlstra <peterz@infradead.org> > > > Signed-off-by: Andrii Nakryiko <andrii@kernel.org> > > > --- > > > 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. > > > > > 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) <mhiramat@kernel.org>
On Tue, 12 Nov 2024 10:09:58 -0800 Andrii Nakryiko <andrii.nakryiko@gmail.com> wrote: > On Mon, Nov 11, 2024 at 5:05 PM Suren Baghdasaryan <surenb@google.com> wrote: > > > > On Mon, Nov 11, 2024 at 4:28 PM Masami Hiramatsu <mhiramat@kernel.org> wrote: > > > > > > On Sun, 27 Oct 2024 18:08:18 -0700 > > > Andrii Nakryiko <andrii@kernel.org> 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 <oleg@redhat.com> > > > > Suggested-by: Matthew Wilcox <willy@infradead.org> > > > > Suggested-by: Peter Zijlstra <peterz@infradead.org> > > > > Signed-off-by: Andrii Nakryiko <andrii@kernel.org> > > > > --- > > > > 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) <mhiramat@kernel.org> 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) <mhiramat@kernel.org>
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 + */ + 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); + 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) {
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). Reviewed-by: Oleg Nesterov <oleg@redhat.com> Suggested-by: Matthew Wilcox <willy@infradead.org> Suggested-by: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Andrii Nakryiko <andrii@kernel.org> --- kernel/events/uprobes.c | 45 +++++++++++++++++++++++++++++++++++++++++ 1 file changed, 45 insertions(+)