Re: [PATCH v4 3.0-rc2-tip 7/22] 7: uprobes: mmap and fork hooks.

Srikar Dronamraju
2011-06-24T02:15:57Z

>
> so I am thinking of a solution that includes most of your ideas along
> with using i_mmap_mutex in mmap_uprobe path.
>

Addressing Peter's comments given on irc wrt i_mmap_mutex.

/*
Changes:
1. Uses inode->i_mutex instead of uprobes_mutex.
2. Now along with vma rma walk, i_mmap_mutex is even held when we do deletion of uprobes into RB tree.
3. mmap_uprobe takes i_mmap_mutex.

Advantages:
1. No need to drop mmap_sem.
2. Now register/unregister can run in parallel.
3.
*/

void _unregister_uprobe(...)
{
if (!del_consumer(...)) { // includes tree removal on last consumer
return;
}
if (uprobe->consumers)
return;

mutex_lock(&mapping->i_mmap_mutex); //sync with mmap.
vma_prio_tree_foreach() {
// create list
}

mutex_unlock(&mapping->i_mmap_mutex);

list_for_each_entry_safe() {
// remove from list
down_read(&mm->mmap_sem);
remove_breakpoint(); // unconditional, if it wasn't there
up_read(&mm->mmap_sem);
}

mutex_lock(&mapping->i_mmap_mutex);
delete_uprobe(uprobe);
mutex_unlock(&mapping->i_mmap_mutex);

inode->uprobes_count--;
mutex_unlock(&inode->i_mutex);
}

int register_uprobe(...)
{
uprobe = alloc_uprobe(...); // find or insert in tree

mutex_lock(&inode->i_mutex); // sync with register/unregister
if (uprobe->consumers) {
add_consumer();
goto put_unlock;
}
add_consumer();
inode->uprobes_count++;
mutex_lock(&mapping->i_mmap_mutex); //sync with mmap.
vma_prio_tree_foreach(..) {
// get mm ref, add to list blah blah
}

mutex_unlock(&mapping->i_mmap_mutex);
list_for_each_entry_safe() {
if (ret) {
// del from list etc..
//
continue;
}
down_read(mm->mmap_sem);
ret = install_breakpoint();
up_read(..);
// del from list etc..
//
if (ret && (ret == -ESRCH || ret == -EEXIST))
ret = 0;
}

if (ret)
_unregister_uprobe();

put_unlock:
mutex_unlock(&inode->i_mutex);
put_uprobe(uprobe);
return ret;
}

void unregister_uprobe(...)
{
mutex_lock(&inode->i_mutex); // sync with register/unregister
uprobe = find_uprobe(); // ref++
_unregister_uprobe();
mutex_unlock(&inode->i_mutex);
put_uprobe(uprobe);
}

int mmap_uprobe(struct vm_area_struct *vma)
{
struct list_head tmp_list;
struct uprobe *uprobe, *u;
struct mm_struct *mm;
struct inode *inode;
int ret = 0;

if (!valid_vma(vma))
return ret; /* Bail-out */

mm = vma->vm_mm;
inode = vma->vm_file->f_mapping->host;
if (inode->uprobes_count)
return ret;
__iget(inode);

INIT_LIST_HEAD(&tmp_list);

mutex_lock(&mapping->i_mmap_mutex);
add_to_temp_list(vma, inode, &tmp_list);
list_for_each_entry_safe(uprobe, u, &tmp_list, pending_list) {
loff_t vaddr;

list_del(&uprobe->pending_list);
if (ret)
continue;

vaddr = vma->vm_start + uprobe->offset;
vaddr -= vma->vm_pgoff << PAGE_SHIFT;
ret = install_breakpoint(mm, uprobe, vaddr);

if (ret && (ret == -ESRCH || ret == -EEXIST))
ret = 0;
}

mutex_unlock(&mapping->i_mmap_mutex);
iput(inode);
return ret;
}

int munmap_uprobe(struct vm_area_struct *vma)
{
struct list_head tmp_list;
struct uprobe *uprobe, *u;
struct mm_struct *mm;
struct inode *inode;
int ret = 0;

if (!valid_vma(vma))
return ret; /* Bail-out */

mm = vma->vm_mm;
inode = vma->vm_file->f_mapping->host;
if (inode->uprobes_count)
return ret;

// walk thro RB tree and decrement mm->uprobes_count
walk_rbtree_and_dec_uprobes_count(); //hold treelock.

return ret;
}