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ceph: get snap_rwsem read lock in handle_cap_export for ceph_add_cap
ceph_add_cap says in its function documentation that the caller should hold the read lock on the session snap_rwsem. Furthermore, not only ceph_add_cap needs that lock, when it calls to ceph_lookup_snap_realm it eventually calls ceph_get_snap_realm which states via lockdep that snap_rwsem needs to be held. handle_cap_export calls ceph_add_cap without that mdsc->snap_rwsem held. Thus, since ceph_get_snap_realm and ceph_add_cap both need the lock, the common place to acquire that lock is inside handle_cap_export. Signed-off-by: Niels Dossche <dossche.niels@gmail.com> Reviewed-by: Xiubo Li <xiubli@redhat.com> Reviewed-by: Jeff Layton <jlayton@kernel.org> Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
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@ -3870,6 +3870,7 @@ static void handle_cap_export(struct inode *inode, struct ceph_mds_caps *ex,
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dout("handle_cap_export inode %p ci %p mds%d mseq %d target %d\n",
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inode, ci, mds, mseq, target);
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retry:
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down_read(&mdsc->snap_rwsem);
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spin_lock(&ci->i_ceph_lock);
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cap = __get_cap_for_mds(ci, mds);
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if (!cap || cap->cap_id != le64_to_cpu(ex->cap_id))
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@ -3933,6 +3934,7 @@ retry:
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}
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spin_unlock(&ci->i_ceph_lock);
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up_read(&mdsc->snap_rwsem);
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mutex_unlock(&session->s_mutex);
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/* open target session */
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@ -3958,6 +3960,7 @@ retry:
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out_unlock:
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spin_unlock(&ci->i_ceph_lock);
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up_read(&mdsc->snap_rwsem);
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mutex_unlock(&session->s_mutex);
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if (tsession) {
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mutex_unlock(&tsession->s_mutex);
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