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Message-Id: <20180301230741.bf15b2ab4c4913303e54884a@kernel.org>
Date: Thu, 1 Mar 2018 23:07:41 +0900
From: Masami Hiramatsu <mhiramat@...nel.org>
To: Ravi Bangoria <ravi.bangoria@...ux.vnet.ibm.com>
Cc: peterz@...radead.org, mingo@...hat.com, acme@...nel.org,
alexander.shishkin@...ux.intel.com, jolsa@...hat.com,
namhyung@...nel.org, linux-kernel@...r.kernel.org,
rostedt@...dmis.org, ananth@...ux.vnet.ibm.com,
naveen.n.rao@...ux.vnet.ibm.com, srikar@...ux.vnet.ibm.com,
oleg@...hat.com
Subject: Re: [RFC 3/4] trace_uprobe: Support SDT markers having semaphore
On Wed, 28 Feb 2018 13:23:44 +0530
Ravi Bangoria <ravi.bangoria@...ux.vnet.ibm.com> wrote:
> Userspace Statically Defined Tracepoints[1] are dtrace style markers
> inside userspace applications. These markers are added by developer at
> important places in the code. Each marker source expands to a single
> nop instruction in the compiled code but there may be additional
> overhead for computing the marker arguments which expands to couple of
> instructions. If this computaion is quite more, execution of it can be
> ommited by runtime if() condition when no one is tracing on the marker:
>
> if (semaphore > 0) {
> Execute marker instructions;
> }
>
> Default value of semaphore is 0. Tracer has to increment the semaphore
> before recording on a marker and decrement it at the end of tracing.
>
> Implement the semaphore flip logic in trace_uprobe, leaving core uprobe
> infrastructure as is, except one new callback from uprobe_mmap() to
> trace_uprobe.
>
> There are two major scenarios while enabling the marker,
> 1. Trace already running process. In this case, find all suitable
> processes and increment the semaphore value in them.
> 2. Trace is already enabled when target binary is executed. In this
> case, all mmaps will get notified to trace_uprobe and trace_uprobe
> will increment the semaphore if corresponding uprobe is enabled.
>
> At the time of disabling probes, decrement semaphore in all existing
> target processes.
>
> Signed-off-by: Ravi Bangoria <ravi.bangoria@...ux.vnet.ibm.com>
> ---
> include/linux/uprobes.h | 2 +
> kernel/events/uprobes.c | 5 ++
> kernel/trace/trace_uprobe.c | 145 ++++++++++++++++++++++++++++++++++++++++++++
> 3 files changed, 152 insertions(+)
>
> diff --git a/include/linux/uprobes.h b/include/linux/uprobes.h
> index 06c169e..04e9d57 100644
> --- a/include/linux/uprobes.h
> +++ b/include/linux/uprobes.h
> @@ -121,6 +121,8 @@ struct uprobe_map_info {
> unsigned long vaddr;
> };
>
> +extern void (*uprobe_mmap_callback)(struct vm_area_struct *vma);
> +
> extern int set_swbp(struct arch_uprobe *aup, struct mm_struct *mm, unsigned long vaddr);
> extern int set_orig_insn(struct arch_uprobe *aup, struct mm_struct *mm, unsigned long vaddr);
> extern bool is_swbp_insn(uprobe_opcode_t *insn);
> diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
> index 56dd7af..81d8aaf 100644
> --- a/kernel/events/uprobes.c
> +++ b/kernel/events/uprobes.c
> @@ -1051,6 +1051,8 @@ static void build_probe_list(struct inode *inode,
> spin_unlock(&uprobes_treelock);
> }
>
> +void (*uprobe_mmap_callback)(struct vm_area_struct *vma) = NULL;
> +
> /*
> * Called from mmap_region/vma_adjust with mm->mmap_sem acquired.
> *
> @@ -1063,6 +1065,9 @@ int uprobe_mmap(struct vm_area_struct *vma)
> struct uprobe *uprobe, *u;
> struct inode *inode;
>
> + if (vma->vm_flags & VM_WRITE && uprobe_mmap_callback)
> + uprobe_mmap_callback(vma);
> +
> if (no_uprobe_events() || !valid_vma(vma, true))
> return 0;
>
> diff --git a/kernel/trace/trace_uprobe.c b/kernel/trace/trace_uprobe.c
> index 40592e7b..d14aafc 100644
> --- a/kernel/trace/trace_uprobe.c
> +++ b/kernel/trace/trace_uprobe.c
> @@ -25,6 +25,7 @@
> #include <linux/namei.h>
> #include <linux/string.h>
> #include <linux/rculist.h>
> +#include <linux/sched/mm.h>
>
> #include "trace_probe.h"
>
> @@ -58,6 +59,7 @@ struct trace_uprobe {
> struct inode *inode;
> char *filename;
> unsigned long offset;
> + unsigned long sdt_offset; /* sdt semaphore offset */
> unsigned long nhit;
> struct trace_probe tp;
> };
> @@ -502,6 +504,16 @@ static int create_trace_uprobe(int argc, char **argv)
> for (i = 0; i < argc && i < MAX_TRACE_ARGS; i++) {
> struct probe_arg *parg = &tu->tp.args[i];
>
> + /* This is not really an argument. */
> + if (argv[i][0] == '*') {
> + ret = kstrtoul(&(argv[i][1]), 0, &tu->sdt_offset);
> + if (ret) {
> + pr_info("Invalid semaphore address.\n");
> + goto error;
> + }
> + continue;
> + }
So, this part should be done with parsing probe-point as I pointed.
> +
> /* Increment count for freeing args in error case */
> tu->tp.nr_args++;
>
> @@ -894,6 +906,131 @@ static void uretprobe_trace_func(struct trace_uprobe *tu, unsigned long func,
> return trace_handle_return(s);
> }
>
> +static bool sdt_valid_vma(struct trace_uprobe *tu, struct vm_area_struct *vma)
> +{
> + unsigned long vaddr = offset_to_vaddr(vma, tu->sdt_offset);
> +
> + return tu->sdt_offset &&
> + vma->vm_file &&
> + file_inode(vma->vm_file) == tu->inode &&
> + vma->vm_flags & VM_WRITE &&
> + vma->vm_start <= vaddr &&
> + vma->vm_end > vaddr;
> +}
> +
> +static struct vm_area_struct *
> +sdt_find_vma(struct mm_struct *mm, struct trace_uprobe *tu)
> +{
> + struct vm_area_struct *tmp;
> +
> + for (tmp = mm->mmap; tmp != NULL; tmp = tmp->vm_next)
> + if (sdt_valid_vma(tu, tmp))
> + return tmp;
> +
> + return NULL;
> +}
> +
> +static int
> +sdt_update_sem(struct mm_struct *mm, unsigned long vaddr, short val)
> +{
> + struct page *page;
> + struct vm_area_struct *vma;
> + int ret = 0;
> + unsigned short orig = 0;
> +
> + if (vaddr == 0)
> + return -EINVAL;
> +
> + ret = get_user_pages_remote(NULL, mm, vaddr, 1,
> + FOLL_FORCE | FOLL_WRITE, &page, &vma, NULL);
> + if (ret <= 0)
> + return ret;
> +
> + copy_from_page(page, vaddr, &orig, sizeof(orig));
> + orig += val;
> + copy_to_page(page, vaddr, &orig, sizeof(orig));
> + put_page(page);
> + return 0;
> +}
> +
> +/*
> + * TODO: Adding this defination in include/linux/uprobes.h throws
> + * warnings about address_sapce. Adding it here for the time being.
> + */
> +struct uprobe_map_info *build_uprobe_map_info(struct address_space *mapping, loff_t offset, bool is_register);
> +
> +static void sdt_increment_sem(struct trace_uprobe *tu)
> +{
> + struct uprobe_map_info *info;
> + struct vm_area_struct *vma;
> + unsigned long vaddr;
> +
> + uprobe_start_dup_mmap();
> + info = build_uprobe_map_info(tu->inode->i_mapping, tu->sdt_offset, false);
> + if (IS_ERR(info))
> + goto out;
> +
> + while (info) {
> + down_write(&info->mm->mmap_sem);
> + vma = sdt_find_vma(info->mm, tu);
> + if (!vma)
> + goto cont;
> +
> + vaddr = offset_to_vaddr(vma, tu->sdt_offset);
> + sdt_update_sem(info->mm, vaddr, 1);
> +
> +cont:
Why would you use goto here?
Thank you,
> + up_write(&info->mm->mmap_sem);
> + mmput(info->mm);
> + info = free_uprobe_map_info(info);
> + }
> +
> +out:
> + uprobe_end_dup_mmap();
> +}
> +
> +/* Called with down_write(&vma->vm_mm->mmap_sem) */
> +void trace_uprobe_mmap_callback(struct vm_area_struct *vma)
> +{
> + struct trace_uprobe *tu;
> + unsigned long vaddr;
> +
> + mutex_lock(&uprobe_lock);
> + list_for_each_entry(tu, &uprobe_list, list) {
> + if (!sdt_valid_vma(tu, vma) ||
> + !trace_probe_is_enabled(&tu->tp))
> + continue;
> +
> + vaddr = offset_to_vaddr(vma, tu->sdt_offset);
> + sdt_update_sem(vma->vm_mm, vaddr, 1);
> + }
> + mutex_unlock(&uprobe_lock);
> +}
> +
> +static void sdt_decrement_sem(struct trace_uprobe *tu)
> +{
> + struct vm_area_struct *vma;
> + unsigned long vaddr;
> + struct uprobe_map_info *info;
> +
> + info = build_uprobe_map_info(tu->inode->i_mapping, tu->sdt_offset, false);
> + if (IS_ERR(info))
> + return;
> +
> + while (info) {
> + down_write(&info->mm->mmap_sem);
> + vma = sdt_find_vma(info->mm, tu);
> + if (vma) {
> + vaddr = offset_to_vaddr(vma, tu->sdt_offset);
> + sdt_update_sem(info->mm, vaddr, -1);
> + }
> + up_write(&info->mm->mmap_sem);
> +
> + mmput(info->mm);
> + info = free_uprobe_map_info(info);
> + }
> +}
> +
> typedef bool (*filter_func_t)(struct uprobe_consumer *self,
> enum uprobe_filter_ctx ctx,
> struct mm_struct *mm);
> @@ -939,6 +1076,9 @@ typedef bool (*filter_func_t)(struct uprobe_consumer *self,
> if (ret)
> goto err_buffer;
>
> + if (tu->sdt_offset)
> + sdt_increment_sem(tu);
> +
> return 0;
>
> err_buffer:
> @@ -979,6 +1119,9 @@ typedef bool (*filter_func_t)(struct uprobe_consumer *self,
>
> WARN_ON(!uprobe_filter_is_empty(&tu->filter));
>
> + if (tu->sdt_offset)
> + sdt_decrement_sem(tu);
> +
> uprobe_unregister(tu->inode, tu->offset, &tu->consumer);
> tu->tp.flags &= file ? ~TP_FLAG_TRACE : ~TP_FLAG_PROFILE;
>
> @@ -1353,6 +1496,8 @@ static __init int init_uprobe_trace(void)
> /* Profile interface */
> trace_create_file("uprobe_profile", 0444, d_tracer,
> NULL, &uprobe_profile_ops);
> +
> + uprobe_mmap_callback = trace_uprobe_mmap_callback;
> return 0;
> }
>
> --
> 1.8.3.1
>
--
Masami Hiramatsu <mhiramat@...nel.org>
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