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    SubjectRe: [PATCH] [13/16] HWPOISON: The high level memory error handler in the VM v5
    On Wed, Jun 03, 2009 at 08:46:47PM +0200, Andi Kleen wrote:
    > +static int me_pagecache_clean(struct page *p, unsigned long pfn)
    > +{
    > + struct address_space *mapping;
    > +
    > + if (!isolate_lru_page(p))
    > + page_cache_release(p);
    > +
    > + /*
    > + * Now truncate the page in the page cache. This is really
    > + * more like a "temporary hole punch"
    > + * Don't do this for block devices when someone else
    > + * has a reference, because it could be file system metadata
    > + * and that's not safe to truncate.
    > + */
    > + mapping = page_mapping(p);
    > + if (mapping && S_ISBLK(mapping->host->i_mode) && page_count(p) > 1) {
    > + printk(KERN_ERR
    > + "MCE %#lx: page looks like a unsupported file system metadata page\n",
    > + pfn);
    > + return FAILED;
    > + }

    page_count check is racy. Hmm, S_ISBLK should handle xfs's private mapping.
    AFAIK btrfs has a similar private mapping but a quick grep does not show
    up S_IFBLK anywhere, so I don't know what the situation is there.

    Unfortunately though, the linear mapping is not the only metadata mapping
    a filesystem might have. Many work on directories in seperate mappings
    (ext2, for example, which is where I first looked and will still oops with
    your check).

    Also, others may have other interesting inodes they use for metadata. Do
    any of them go through the pagecache? I dont know. The ext3 journal,
    for example? How does that work?

    Unfortunately I don't know a good way to detect regular data mappings
    easily. Ccing linux-fsdevel. Until that is worked out, you'd need to
    use the safe pagecache invalidate rather than unsafe truncate.


    > + if (mapping) {
    > + truncate_inode_page(mapping, p);
    > + if (page_has_private(p) && !try_to_release_page(p, GFP_NOIO)) {
    > + pr_debug(KERN_ERR "MCE %#lx: failed to release buffers\n",
    > + pfn);
    > + return FAILED;
    > + }
    > + }
    > + return RECOVERED;
    > +}


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