lkml.org 
[lkml]   [2012]   [Jul]   [30]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
Subject[tip:perf/core] uprobes: Clean up and document write_opcode()-> lock_page(old_page)
Commit-ID:  9f92448ceeea5326db7d114005a7e7ac03904edf
Gitweb: http://git.kernel.org/tip/9f92448ceeea5326db7d114005a7e7ac03904edf
Author: Oleg Nesterov <oleg@redhat.com>
AuthorDate: Sun, 29 Jul 2012 20:22:20 +0200
Committer: Ingo Molnar <mingo@kernel.org>
CommitDate: Mon, 30 Jul 2012 11:27:20 +0200

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>
---
kernel/events/uprobes.c | 27 ++++++++++++++-------------
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))

\
 
 \ /
  Last update: 2012-07-30 17:02    [from the cache]
©2003-2011 Jasper Spaans