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    SubjectRe: [PATCH] aio: fix kernel bug when page is temporally busy
    On Fri, 9 Feb 2007, Ananiev, Leonid I wrote:

    > Fix "Kernel BUG at fs/aio.c:509". Return EIOCBRETRY but not EIO if page
    > is busy.

    I am currently also hunting in this area, and I think there is something
    strange in generic_file_aio_read(). This seems strange:

    for (seg = 0; seg < nr_segs; seg++) {
    read_descriptor_t desc;

    desc.written = 0;
    desc.arg.buf = iov[seg].iov_base;
    desc.count = iov[seg].iov_len;
    if (desc.count == 0)
    continue;
    desc.error = 0;

    do_generic_file_read(filp,ppos,&desc,file_read_actor);
    retval += desc.written;
    if (desc.error) {
    retval = retval ?: desc.error;
    break;
    }
    }

    So this code propagates desc.error back to caller _only if_ all of the
    previous segments had desc.written == 0. Which is bogus - we need to
    propagate -EIOCBRETRY as soon as any of the do_generic_file_read()
    returned it, so that the caller is aware of requests being queued.

    I think something like this would be appropriate

    [PATCH] AIO: handle return value from do_generic_file_read() properly

    generic_file_aio_read() doesn't always propagate error return value from
    do_generic_file_read(). Namely handling of -EIOCBRETRY is important, because
    aio_run_iocb() relies on this return value being always properly propagated
    to it.

    Signed-off-by: Jiri Kosina <jkosina@suse.cz>

    ---

    mm/filemap.c | 2 +-
    1 files changed, 1 insertions(+), 1 deletions(-)

    diff --git a/mm/filemap.c b/mm/filemap.c
    index 8332c77..5ce76ce 100644
    --- a/mm/filemap.c
    +++ b/mm/filemap.c
    @@ -1204,7 +1204,7 @@ generic_file_aio_read(struct kiocb *iocb, const struct iovec *iov,
    do_generic_file_read(filp,ppos,&desc,file_read_actor);
    retval += desc.written;
    if (desc.error) {
    - retval = retval ?: desc.error;
    + retval = desc.error;
    break;
    }
    }
    --
    Jiri Kosina
    -
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