Commit 77fc4af1 authored May 29, 2012 by Oleg Nesterov Committed by Ingo Molnar Jun 06, 2012

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>

parent d790d346

kernel/events/uprobes.c

+4 −4

Original line number	Diff line number	Diff line
		@@ -853,12 +853,12 @@ static int register_for_each_vma(struct uprobe *uprobe, bool is_register)
		}

		mm = vi->mm;
		down_read(&mm->mmap_sem);
		down_write(&mm->mmap_sem);
		vma = find_vma(mm, (unsigned long)vi->vaddr);
		if (!vma \|\| !valid_vma(vma, is_register)) {
		list_del(&vi->probe_list);
		kfree(vi);
		up_read(&mm->mmap_sem);
		up_write(&mm->mmap_sem);
		mmput(mm);
		continue;
		}
		@@ -867,7 +867,7 @@ static int register_for_each_vma(struct uprobe *uprobe, bool is_register)
		vaddr != vi->vaddr) {
		list_del(&vi->probe_list);
		kfree(vi);
		up_read(&mm->mmap_sem);
		up_write(&mm->mmap_sem);
		mmput(mm);
		continue;
		}
		@@ -877,7 +877,7 @@ static int register_for_each_vma(struct uprobe *uprobe, bool is_register)
		else
		remove_breakpoint(uprobe, mm, vi->vaddr);

		up_read(&mm->mmap_sem);
		up_write(&mm->mmap_sem);
		mmput(mm);
		if (is_register) {
		if (ret && ret == -EEXIST)

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