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Commit 9f92448c authored by Oleg Nesterov's avatar Oleg Nesterov Committed by Ingo Molnar
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uprobes: Clean up and document write_opcode()->lock_page(old_page) 



The comment above write_opcode()->lock_page(old_page) tells
about the race with do_wp_page(). I don't really understand
which exactly race it means, but afaics this lock_page() was not
enough to close all races with do_wp_page().

Anyway, since:

   77fc4af1 uprobes: Change register_for_each_vma() to take mm->mmap_sem for writing

this code is always called with ->mmap_sem held for writing,
so we can forget about do_wp_page().

However, we can't simply remove this lock_page(), and the only
(afaics) reason is __replace_page()->try_to_free_swap().

Nothing in write_opcode() needs it, move it into
__replace_page() and fix the comment.

Signed-off-by: default avatarOleg Nesterov <oleg@redhat.com>
Acked-by: Srikar Dronamraju <srikar.vnet.ibm.com>
Cc: Anton Arapov <anton@redhat.com>
Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Link: http://lkml.kernel.org/r/20120729182220.GA20322@redhat.com


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 089ba999

kernel/events/uprobes.c

+14 −13
Original line number Diff line number Diff line
@@ -139,10 +139,15 @@ static int __replace_page(struct vm_area_struct *vma, unsigned long addr, 
	struct mm_struct *mm = vma->vm_mm;

	spinlock_t *ptl;

	pte_t *ptep;

	int err;



	/* freeze PageSwapCache() for try_to_free_swap() below */

	lock_page(page);



	err = -EAGAIN;

	ptep = page_check_address(page, mm, addr, &ptl, 0);

	if (!ptep)

		return -EAGAIN;

		goto unlock;



	get_page(kpage);

	page_add_new_anon_rmap(kpage, vma, addr);
@@ -162,7 +167,10 @@ static int __replace_page(struct vm_area_struct *vma, unsigned long addr, 
	put_page(page);

	pte_unmap_unlock(ptep, ptl);



	return 0;

	err = 0;

 unlock:

	unlock_page(page);

	return err;

}



/**
@@ -216,15 +224,10 @@ static int write_opcode(struct arch_uprobe *auprobe, struct mm_struct *mm, 
	ret = -ENOMEM;

	new_page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, vaddr);

	if (!new_page)

		goto put_out;

		goto put_old;



	__SetPageUptodate(new_page);



	/*

	 * lock page will serialize against do_wp_page()'s

	 * PageAnon() handling

	 */

	lock_page(old_page);

	/* copy the page now that we've got it stable */

	vaddr_old = kmap_atomic(old_page);

	vaddr_new = kmap_atomic(new_page);
@@ -237,15 +240,13 @@ static int write_opcode(struct arch_uprobe *auprobe, struct mm_struct *mm, 


	ret = anon_vma_prepare(vma);

	if (ret)

		goto unlock_out;

		goto put_new;



	ret = __replace_page(vma, vaddr, old_page, new_page);



unlock_out:

	unlock_page(old_page);

put_new:

	page_cache_release(new_page);



put_out:

put_old:

	put_page(old_page);



	if (unlikely(ret == -EAGAIN))