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uprobes: Change register_for_each_vma() to take mm->mmap_sem for writing

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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 <[email protected]>
Acked-by: Srikar Dronamraju <[email protected]>
Cc: Ananth N Mavinakayanahalli <[email protected]>
Cc: Anton Arapov <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Masami Hiramatsu <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>
This commit is contained in:
Oleg Nesterov 2012-05-29 21:29:28 +02:00 • committed by Ingo Molnar
commit 77fc4af1b5
1 changed files with 4 additions and 4 deletions
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8
kernel/events/uprobes.c
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@ -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)