Re: [RFC 3/4] trace_uprobe: Support SDT markers having semaphore

[Masami Hiramatsu]

On Wed, 28 Feb 2018 13:23:44 +0530
Ravi Bangoria <ravi.bangoria@xxxxxxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxxxxxx>
> ---
>  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@xxxxxxxxxx>