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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:

   77fc4af1b5 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>
This commit is contained in:
Oleg Nesterov 2012-07-29 20:22:20 +02:00 committed by Ingo Molnar
parent 089ba999dc
commit 9f92448cee
1 changed files with 14 additions and 13 deletions
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27
kernel/events/uprobes.c
View File

@ -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))