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Date: Mon, 26 Sep 2011 15:53:11 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
Cc: Ingo Molnar <mingo@...e.hu>, Steven Rostedt <rostedt@...dmis.org>,
Linux-mm <linux-mm@...ck.org>,
Arnaldo Carvalho de Melo <acme@...radead.org>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Ananth N Mavinakayanahalli <ananth@...ibm.com>,
Hugh Dickins <hughd@...gle.com>,
Christoph Hellwig <hch@...radead.org>,
Jonathan Corbet <corbet@....net>,
Thomas Gleixner <tglx@...utronix.de>,
Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
Oleg Nesterov <oleg@...hat.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Jim Keniston <jkenisto@...ux.vnet.ibm.com>,
Roland McGrath <roland@...k.frob.com>,
Andi Kleen <andi@...stfloor.org>,
LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5 3.1.0-rc4-tip 4/26] uprobes: Define hooks for
mmap/munmap.
> -static int match_uprobe(struct uprobe *l, struct uprobe *r)
> +static int match_uprobe(struct uprobe *l, struct uprobe *r, int *match_inode)
> {
> + /*
> + * if match_inode is non NULL then indicate if the
> + * inode atleast match.
> + */
> + if (match_inode)
> + *match_inode = 0;
> +
> if (l->inode < r->inode)
> return -1;
> if (l->inode > r->inode)
> return 1;
> else {
> + if (match_inode)
> + *match_inode = 1;
> +
> if (l->offset < r->offset)
> return -1;
>
> @@ -75,16 +86,20 @@ static int match_uprobe(struct uprobe *l, struct uprobe *r)
> return 0;
> }
>
> -static struct uprobe *__find_uprobe(struct inode * inode, loff_t offset)
> +static struct uprobe *__find_uprobe(struct inode * inode, loff_t offset,
> + struct rb_node **close_match)
> {
> struct uprobe u = { .inode = inode, .offset = offset };
> struct rb_node *n = uprobes_tree.rb_node;
> struct uprobe *uprobe;
> - int match;
> + int match, match_inode;
>
> while (n) {
> uprobe = rb_entry(n, struct uprobe, rb_node);
> - match = match_uprobe(&u, uprobe);
> + match = match_uprobe(&u, uprobe, &match_inode);
> + if (close_match && match_inode)
> + *close_match = n;
Because:
if (close_match && uprobe->inode == inode)
Isn't good enough? Also, returning an rb_node just seems iffy..
> if (!match) {
> atomic_inc(&uprobe->ref);
> return uprobe;
Why not something like:
+static struct uprobe *__find_uprobe(struct inode * inode, loff_t offset,
bool inode_only)
+{
struct uprobe u = { .inode = inode, .offset = inode_only ? 0 : offset };
+ struct rb_node *n = uprobes_tree.rb_node;
+ struct uprobe *uprobe;
struct uprobe *ret = NULL;
+ int match;
+
+ while (n) {
+ uprobe = rb_entry(n, struct uprobe, rb_node);
+ match = match_uprobe(&u, uprobe);
+ if (!match) {
if (!inode_only)
atomic_inc(&uprobe->ref);
+ return uprobe;
+ }
if (inode_only && uprobe->inode == inode)
ret = uprobe;
+ if (match < 0)
+ n = n->rb_left;
+ else
+ n = n->rb_right;
+
+ }
return ret;
+}
> +/*
> + * For a given inode, build a list of probes that need to be inserted.
> + */
> +static void build_probe_list(struct inode *inode, struct list_head *head)
> +{
> + struct uprobe *uprobe;
> + struct rb_node *n;
> + unsigned long flags;
> +
> + n = uprobes_tree.rb_node;
> + spin_lock_irqsave(&uprobes_treelock, flags);
> + uprobe = __find_uprobe(inode, 0, &n);
> + /*
> + * If indeed there is a probe for the inode and with offset zero,
> + * then lets release its reference. (ref got thro __find_uprobe)
> + */
> + if (uprobe)
> + put_uprobe(uprobe);
The above would make this ^ unneeded.
n = &uprobe->rb_node;
> + for (; n; n = rb_next(n)) {
> + uprobe = rb_entry(n, struct uprobe, rb_node);
> + if (uprobe->inode != inode)
> + break;
> + list_add(&uprobe->pending_list, head);
> + atomic_inc(&uprobe->ref);
> + }
> + spin_unlock_irqrestore(&uprobes_treelock, flags);
> +}
If this ever gets to be a latency issue (linear lookup under spinlock)
you can use a double lock (mutex+spinlock) and require that modification
acquires both but lookups can get away with either.
That way you can do the linear search using a mutex instead of the
spinlock.
> +
> +/*
> + * Called from mmap_region.
> + * called with mm->mmap_sem acquired.
> + *
> + * Return -ve no if we fail to insert probes and we cannot
> + * bail-out.
> + * Return 0 otherwise. i.e :
> + * - successful insertion of probes
> + * - (or) no possible probes to be inserted.
> + * - (or) insertion of probes failed but we can bail-out.
> + */
> +int mmap_uprobe(struct vm_area_struct *vma)
> +{
> + struct list_head tmp_list;
> + struct uprobe *uprobe, *u;
> + struct inode *inode;
> + int ret = 0;
> +
> + if (!valid_vma(vma))
> + return ret; /* Bail-out */
> +
> + inode = igrab(vma->vm_file->f_mapping->host);
> + if (!inode)
> + return ret;
> +
> + INIT_LIST_HEAD(&tmp_list);
> + mutex_lock(&uprobes_mmap_mutex);
> + build_probe_list(inode, &tmp_list);
> + list_for_each_entry_safe(uprobe, u, &tmp_list, pending_list) {
> + loff_t vaddr;
> +
> + list_del(&uprobe->pending_list);
> + if (!ret && uprobe->consumers) {
> + vaddr = vma->vm_start + uprobe->offset;
> + vaddr -= vma->vm_pgoff << PAGE_SHIFT;
> + if (vaddr < vma->vm_start || vaddr >= vma->vm_end)
> + continue;
> + ret = install_breakpoint(vma->vm_mm, uprobe);
> +
> + if (ret && (ret == -ESRCH || ret == -EEXIST))
> + ret = 0;
> + }
> + put_uprobe(uprobe);
> + }
> +
> + mutex_unlock(&uprobes_mmap_mutex);
> + iput(inode);
> + return ret;
> +}
> +
> +static void dec_mm_uprobes_count(struct vm_area_struct *vma,
> + struct inode *inode)
> +{
> + struct uprobe *uprobe;
> + struct rb_node *n;
> + unsigned long flags;
> +
> + n = uprobes_tree.rb_node;
> + spin_lock_irqsave(&uprobes_treelock, flags);
> + uprobe = __find_uprobe(inode, 0, &n);
> +
> + /*
> + * If indeed there is a probe for the inode and with offset zero,
> + * then lets release its reference. (ref got thro __find_uprobe)
> + */
> + if (uprobe)
> + put_uprobe(uprobe);
> + for (; n; n = rb_next(n)) {
> + loff_t vaddr;
> +
> + uprobe = rb_entry(n, struct uprobe, rb_node);
> + if (uprobe->inode != inode)
> + break;
> + vaddr = vma->vm_start + uprobe->offset;
> + vaddr -= vma->vm_pgoff << PAGE_SHIFT;
> + if (vaddr < vma->vm_start || vaddr >= vma->vm_end)
> + continue;
> + atomic_dec(&vma->vm_mm->mm_uprobes_count);
> + }
> + spin_unlock_irqrestore(&uprobes_treelock, flags);
> +}
> +
> +/*
> + * Called in context of a munmap of a vma.
> + */
> +void munmap_uprobe(struct vm_area_struct *vma)
> +{
> + struct inode *inode;
> +
> + if (!valid_vma(vma))
> + return; /* Bail-out */
> +
> + if (!atomic_read(&vma->vm_mm->mm_uprobes_count))
> + return;
> +
> + inode = igrab(vma->vm_file->f_mapping->host);
> + if (!inode)
> + return;
> +
> + dec_mm_uprobes_count(vma, inode);
> + iput(inode);
> + return;
> +}
One has to wonder why mmap_uprobe() can be one function but
munmap_uprobe() cannot.
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