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    Subject[PATCH 5.15 827/846] net: ipa: fix atomic update in ipa_endpoint_replenish()
    Date
    From: Alex Elder <elder@linaro.org>

    commit 6c0e3b5ce94947b311348c367db9e11dcb2ccc93 upstream.

    In ipa_endpoint_replenish(), if an error occurs when attempting to
    replenish a receive buffer, we just quit and try again later. In
    that case we increment the backlog count to reflect that the attempt
    was unsuccessful. Then, if the add_one flag was true we increment
    the backlog again.

    This second increment is not included in the backlog local variable
    though, and its value determines whether delayed work should be
    scheduled. This is a bug.

    Fix this by determining whether 1 or 2 should be added to the
    backlog before adding it in a atomic_add_return() call.

    Reviewed-by: Matthias Kaehlcke <mka@chromium.org>
    Fixes: 84f9bd12d46db ("soc: qcom: ipa: IPA endpoints")
    Signed-off-by: Alex Elder <elder@linaro.org>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    drivers/net/ipa/ipa_endpoint.c | 7 +++----
    1 file changed, 3 insertions(+), 4 deletions(-)

    --- a/drivers/net/ipa/ipa_endpoint.c
    +++ b/drivers/net/ipa/ipa_endpoint.c
    @@ -1067,6 +1067,7 @@ static void ipa_endpoint_replenish(struc
    {
    struct gsi *gsi;
    u32 backlog;
    + int delta;

    if (!endpoint->replenish_enabled) {
    if (add_one)
    @@ -1084,10 +1085,8 @@ static void ipa_endpoint_replenish(struc

    try_again_later:
    /* The last one didn't succeed, so fix the backlog */
    - backlog = atomic_inc_return(&endpoint->replenish_backlog);
    -
    - if (add_one)
    - atomic_inc(&endpoint->replenish_backlog);
    + delta = add_one ? 2 : 1;
    + backlog = atomic_add_return(delta, &endpoint->replenish_backlog);

    /* Whenever a receive buffer transaction completes we'll try to
    * replenish again. It's unlikely, but if we fail to supply even

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