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    Subject[PATCH 4.9 068/137] drbd: narrow rcu_read_lock in drbd_sync_handshake
    Date
    4.9-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    [ Upstream commit d29e89e34952a9ad02c77109c71a80043544296e ]

    So far there was the possibility that we called
    genlmsg_new(GFP_NOIO)/mutex_lock() while holding an rcu_read_lock().

    This included cases like:

    drbd_sync_handshake (acquire the RCU lock)
    drbd_asb_recover_1p
    drbd_khelper
    drbd_bcast_event
    genlmsg_new(GFP_NOIO) --> may sleep

    drbd_sync_handshake (acquire the RCU lock)
    drbd_asb_recover_1p
    drbd_khelper
    notify_helper
    genlmsg_new(GFP_NOIO) --> may sleep

    drbd_sync_handshake (acquire the RCU lock)
    drbd_asb_recover_1p
    drbd_khelper
    notify_helper
    mutex_lock --> may sleep

    While using GFP_ATOMIC whould have been possible in the first two cases,
    the real fix is to narrow the rcu_read_lock.

    Reported-by: Jia-Ju Bai <baijiaju1990@163.com>
    Reviewed-by: Lars Ellenberg <lars.ellenberg@linbit.com>
    Signed-off-by: Roland Kammerer <roland.kammerer@linbit.com>
    Signed-off-by: Jens Axboe <axboe@kernel.dk>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    drivers/block/drbd/drbd_receiver.c | 11 ++++++-----
    1 file changed, 6 insertions(+), 5 deletions(-)

    diff --git a/drivers/block/drbd/drbd_receiver.c b/drivers/block/drbd/drbd_receiver.c
    index 942384f34e22..77d0f80f62f9 100644
    --- a/drivers/block/drbd/drbd_receiver.c
    +++ b/drivers/block/drbd/drbd_receiver.c
    @@ -3421,7 +3421,7 @@ static enum drbd_conns drbd_sync_handshake(struct drbd_peer_device *peer_device,
    enum drbd_conns rv = C_MASK;
    enum drbd_disk_state mydisk;
    struct net_conf *nc;
    - int hg, rule_nr, rr_conflict, tentative;
    + int hg, rule_nr, rr_conflict, tentative, always_asbp;

    mydisk = device->state.disk;
    if (mydisk == D_NEGOTIATING)
    @@ -3472,8 +3472,12 @@ static enum drbd_conns drbd_sync_handshake(struct drbd_peer_device *peer_device,

    rcu_read_lock();
    nc = rcu_dereference(peer_device->connection->net_conf);
    + always_asbp = nc->always_asbp;
    + rr_conflict = nc->rr_conflict;
    + tentative = nc->tentative;
    + rcu_read_unlock();

    - if (hg == 100 || (hg == -100 && nc->always_asbp)) {
    + if (hg == 100 || (hg == -100 && always_asbp)) {
    int pcount = (device->state.role == R_PRIMARY)
    + (peer_role == R_PRIMARY);
    int forced = (hg == -100);
    @@ -3512,9 +3516,6 @@ static enum drbd_conns drbd_sync_handshake(struct drbd_peer_device *peer_device,
    "Sync from %s node\n",
    (hg < 0) ? "peer" : "this");
    }
    - rr_conflict = nc->rr_conflict;
    - tentative = nc->tentative;
    - rcu_read_unlock();

    if (hg == -100) {
    /* FIXME this log message is not correct if we end up here
    --
    2.19.1


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