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    SubjectRe: [PATCH v8 00/17] gfs2: Fix mmap + page fault deadlocks
    Date
    Ted,

    here's an updated version of Dave Hansen's original commit, but note
    that generic/208 won't run on ext4 with data journaling enabled:

    $ MOUNT_OPTIONS='-o data=journal' TEST_DIR=/mnt/test TEST_DEV=/dev/vdb ./tests/generic/208
    QA output created by 208
    208 not run: ext4 data journaling doesn't support O_DIRECT

    Thanks,
    Andreas

    --

    Based on commit 998ef75ddb57 ("fs: do not prefault sys_write() user
    buffer pages") by Dave Hansen <dave.hansen@linux.intel.com>, but:

    * Fix generic_perform_write as well as iomap_write_iter.

    * copy_page_from_iter_atomic() doesn't trigger page faults, so there's no need
    to disable page faults around it [see commit 9e8c2af96e0d ("callers of
    iov_copy_from_user_atomic() don't need pagecache_disable()")].

    * If fault_in_iov_iter_readable() fails to fault in the entire buffer,
    we still want to read everything up to the fault position. This depends on
    commit a6294593e8a1 ("iov_iter: Turn iov_iter_fault_in_readable into
    fault_in_iov_iter_readable").

    Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
    ---
    fs/iomap/buffered-io.c | 20 +++++++-------------
    mm/filemap.c | 20 +++++++-------------
    2 files changed, 14 insertions(+), 26 deletions(-)

    diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
    index 1753c26c8e76..d8809cd9ab31 100644
    --- a/fs/iomap/buffered-io.c
    +++ b/fs/iomap/buffered-io.c
    @@ -744,17 +744,6 @@ static loff_t iomap_write_iter(struct iomap_iter *iter, struct iov_iter *i)
    if (bytes > length)
    bytes = length;

    - /*
    - * Bring in the user page that we'll copy from _first_.
    - * Otherwise there's a nasty deadlock on copying from the
    - * same page as we're writing to, without it being marked
    - * up-to-date.
    - */
    - if (unlikely(fault_in_iov_iter_readable(i, bytes))) {
    - status = -EFAULT;
    - break;
    - }
    -
    status = iomap_write_begin(iter, pos, bytes, &page);
    if (unlikely(status))
    break;
    @@ -777,9 +766,14 @@ static loff_t iomap_write_iter(struct iomap_iter *iter, struct iov_iter *i)
    * halfway through, might be a race with munmap,
    * might be severe memory pressure.
    */
    - if (copied)
    + if (copied) {
    bytes = copied;
    - goto again;
    + goto again;
    + }
    + if (fault_in_iov_iter_readable(i, bytes) != bytes)
    + goto again;
    + status = -EFAULT;
    + break;
    }
    pos += status;
    written += status;
    diff --git a/mm/filemap.c b/mm/filemap.c
    index 4dd5edcd39fd..467cdb7d086d 100644
    --- a/mm/filemap.c
    +++ b/mm/filemap.c
    @@ -3751,17 +3751,6 @@ ssize_t generic_perform_write(struct file *file,
    iov_iter_count(i));

    again:
    - /*
    - * Bring in the user page that we will copy from _first_.
    - * Otherwise there's a nasty deadlock on copying from the
    - * same page as we're writing to, without it being marked
    - * up-to-date.
    - */
    - if (unlikely(fault_in_iov_iter_readable(i, bytes))) {
    - status = -EFAULT;
    - break;
    - }
    -
    if (fatal_signal_pending(current)) {
    status = -EINTR;
    break;
    @@ -3794,9 +3783,14 @@ ssize_t generic_perform_write(struct file *file,
    * halfway through, might be a race with munmap,
    * might be severe memory pressure.
    */
    - if (copied)
    + if (copied) {
    bytes = copied;
    - goto again;
    + goto again;
    + }
    + if (fault_in_iov_iter_readable(i, bytes) != bytes)
    + goto again;
    + status = -EFAULT;
    + break;
    }
    pos += status;
    written += status;
    --
    2.26.3
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