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    SubjectRe: [discuss] Re: 2.6.16-rc5-mm3: spinlock bad magic on CPU#0 on AMD64
    Andi Kleen <ak@suse.de> wrote:
    >
    > > Still. It seems that what's happened is that we took a pagefault while
    > > reiserfs had a transaction open. The fault is against a mmapped ext3 file
    > > and we ended up in the recently-reworked ext3_get_block() which tests
    > > journal_current_handle() to work out whether we're in a write or a read.
    > > oops. The presence of reiserfs journal_info makes it decide it's a write,
    > > not a read so it starts treating a reiserfs journal_info as an ext3 one.
    > >
    > > The code used to work OK because it was only for direct-IO, which doesn't
    > > get recurred into like this. But it got used for regular I/O in -mm.
    >
    > Oops. Can this happen in more situations?

    I don't _think_ so, but it's pretty scary. The code's been this way for a
    while.

    Typical scenario:

    reiserfs_journal_start - sets current->journal_info
    copy_from_user
    pagefault
    ext3_readpages()

    As long as ext3_readpage[s]() doesn't try to start a transaction we're OK.
    And it shouldn't, if create==0.

    Fortunately filemap_nopage() doesn't do atime updates. If it did, things
    would get messy.

    We do have deadlock possibilities in there - filemap_nopage() does
    lock_page() inside journal_start(), whereas generic_file_write() does
    journal_start() inside lock_page(). Chris Mason and I have stared
    unhappily at that a few times. Hard to fix.

    But I don't _think_ we have any more journal_start() recursions like this -
    ext3 tends to get pretty noisy if it detects that in unexpected places.

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