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SubjectRe: [PATCH] shmem: call set_page_dirty() with locked page
On Wed, 15 Jul 2009, Wu Fengguang wrote:
> shmem: call set_page_dirty() with locked page
>
> The dirtying of page and set_page_dirty() can be moved into the page lock.
>
> - In shmem_write_end(), the page was dirtied while the page lock was held,
> but it's being marked dirty just after dropping the page lock.
> - In shmem_symlink(), both dirtying and marking can be moved into page lock.
>
> It's valuable for the hwpoison code to know whether one bad page can be dropped
> without losing data. It mainly judges by testing the PG_dirty bit after taking
> the page lock. So it becomes important that the dirtying of page and the
> marking of dirtiness are both done inside the page lock. Which is a common
> practice, but sadly not a rule.
>
> The noticeable exceptions are
> - mapped pages
> - pages with buffer_heads
> The above pages could go dirty at any time. Fortunately the hwpoison will
> unmap the page and release the buffer_heads beforehand anyway.
>
> Many other types of pages (eg. metadata pages) can also be dirtied at will by
> their owners, the hwpoison code cannot do meaningful things to them anyway.
> Only the dirtiness of pagecache pages owned by regular files are interested.
>
> CC: Hugh Dickins <hugh@veritas.com>

Ah, those were the days... ;)

> Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>

Acked-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>

> ---
> mm/shmem.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> --- linux.orig/mm/shmem.c
> +++ linux/mm/shmem.c
> @@ -1630,8 +1630,8 @@ shmem_write_end(struct file *file, struc
> if (pos + copied > inode->i_size)
> i_size_write(inode, pos + copied);
>
> - unlock_page(page);
> set_page_dirty(page);
> + unlock_page(page);
> page_cache_release(page);
>
> return copied;
> @@ -1968,13 +1968,13 @@ static int shmem_symlink(struct inode *d
> iput(inode);
> return error;
> }
> - unlock_page(page);
> inode->i_mapping->a_ops = &shmem_aops;
> inode->i_op = &shmem_symlink_inode_operations;
> kaddr = kmap_atomic(page, KM_USER0);
> memcpy(kaddr, symname, len);
> kunmap_atomic(kaddr, KM_USER0);
> set_page_dirty(page);
> + unlock_page(page);
> page_cache_release(page);
> }
> if (dir->i_mode & S_ISGID)


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