Messages in this thread | | | Subject | Re: [PATCH v7 3.2-rc2 4/30] uprobes: Define hooks for mmap/munmap. | From | Peter Zijlstra <> | Date | Thu, 24 Nov 2011 15:13:37 +0100 |
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On Thu, 2011-11-24 at 19:17 +0530, Srikar Dronamraju wrote: > * Peter Zijlstra <peterz@infradead.org> [2011-11-23 19:10:12]: > > > On Fri, 2011-11-18 at 16:37 +0530, Srikar Dronamraju wrote: > > > + ret = install_breakpoint(vma->vm_mm, uprobe); > > > + if (ret == -EEXIST) { > > > + atomic_inc(&vma->vm_mm->mm_uprobes_count); > > > + ret = 0; > > > + } > > > > Aren't you double counting that probe position here? The one that raced > > you to inserting it will also have incremented that counter, no? > > > > No we arent. > Because register_uprobe can never race with mmap_uprobe and register > before mmap_uprobe registers .(Once we start mmap_region, > register_uprobe waits for the read_lock of mmap_sem.)
Still doesn't make any sense. Since you don't increment on success, one has to assume install_breakpoint() will cause an increment. Therefore, when we encounter -EEXIST we'll already have accounted for this mm,inode,offset combination.
But I'll have another look at it, maybe I'm missing something obvious :-)
> And we badly need this for mmap_uprobe case. Because when we do mremap, > or vma_adjust(), we do a munmap_uprobe() followed by mmap_uprobe() which > would have decremented the count but not removed it. So when we do a > mmap_uprobe, we need to increment the count.
Well I see why the count needs to be correct, that's not the issue.
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