uprobes: Clean up and document write_opcode()->lock_page(old_page) (9f92448c) · Commits · 戴 / test

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: 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:

Oleg 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:

Ingo Molnar <mingo@kernel.org>

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 @@ retry:
		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 @@ retry:

		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))

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