uprobes: Change register_for_each_vma() to take mm->mmap_sem for writing
Change register_for_each_vma() to take mm->mmap_sem for writing. This is a bit unfortunate but hopefully not too bad, this is the slow path anyway. This is needed to ensure that find_active_uprobe() can not race with uprobe_register() which adds the new bp at the same bp_vaddr, after find_uprobe() fails and before is_swbp_at_addr_fast() checks the memory. IOW, this is needed to ensure that if find_active_uprobe() returns NULL but is_swbp == true, we can safely assume that it was the "normal" int3 and we should send SIGTRAP. There is another reason for this change. We are going to replace uprobes_state->count with MMF_ flags set by register/unregister and cleared by find_active_uprobe(), and set/clear shouldn't race with each other. Signed-off-by: Oleg Nesterov <oleg@redhat.com> Acked-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com> Cc: Ananth N Mavinakayanahalli <ananth@in.ibm.com> Cc: Anton Arapov <anton@redhat.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com> Cc: Peter Zijlstra <peterz@infradead.org> Link: http://lkml.kernel.org/r/20120529192928.GE8057@redhat.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
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@ -853,12 +853,12 @@ static int register_for_each_vma(struct uprobe *uprobe, bool is_register)
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}
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mm = vi->mm;
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down_read(&mm->mmap_sem);
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down_write(&mm->mmap_sem);
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vma = find_vma(mm, (unsigned long)vi->vaddr);
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if (!vma || !valid_vma(vma, is_register)) {
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list_del(&vi->probe_list);
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kfree(vi);
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up_read(&mm->mmap_sem);
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up_write(&mm->mmap_sem);
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mmput(mm);
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continue;
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}
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@ -867,7 +867,7 @@ static int register_for_each_vma(struct uprobe *uprobe, bool is_register)
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vaddr != vi->vaddr) {
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list_del(&vi->probe_list);
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kfree(vi);
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up_read(&mm->mmap_sem);
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up_write(&mm->mmap_sem);
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mmput(mm);
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continue;
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}
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@ -877,7 +877,7 @@ static int register_for_each_vma(struct uprobe *uprobe, bool is_register)
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else
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remove_breakpoint(uprobe, mm, vi->vaddr);
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up_read(&mm->mmap_sem);
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up_write(&mm->mmap_sem);
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mmput(mm);
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if (is_register) {
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if (ret && ret == -EEXIST)
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