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authorOleg Nesterov <oleg@redhat.com>2012-07-29 20:22:20 +0200
committerIngo Molnar <mingo@kernel.org>2012-07-30 11:27:20 +0200
commit9f92448ceeea5326db7d114005a7e7ac03904edf (patch)
tree42bd61d15b445d8677806adeadae99767094386c
parent089ba999dc881a7549d97c55ac9e0052d061867d (diff)
downloadop-kernel-dev-9f92448ceeea5326db7d114005a7e7ac03904edf.zip
op-kernel-dev-9f92448ceeea5326db7d114005a7e7ac03904edf.tar.gz
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: 77fc4af1b59d 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>
-rw-r--r--kernel/events/uprobes.c27
1 files changed, 14 insertions, 13 deletions
diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index 23c562b7..5db150b 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -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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