The Fc cap refs is no-zero(get_cap_ref by a previous readahead).
Fc cap is being revoked by the mds, and in handle_cap_grant it misses to call check_caps to update cap->issued and cap->implemented
Then a new read operation comes, and in Client::get_caps the reader wants a Fc cap, it will wait for a notification after the Fc revocation finished.
So after the readahead finished, it calls put_cap_ref to released Fc cap，whilch should notify the waiting reader after check_caps

    Fixes: https://tracker.ceph.com/issues/65971
    Signed-off-by: Tod Chen <chentao.2022@bytedance.com>

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