Messages in this thread | | | Date | Thu, 24 Nov 2011 19:17:42 +0530 | From | Srikar Dronamraju <> | Subject | Re: [PATCH v7 3.2-rc2 4/30] uprobes: Define hooks for mmap/munmap. |
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* 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.)
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.
-- Thanks and regards Srikar
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