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    Subject[tip:locking/core] locking/atomics, firmware/ivc: Convert ACCESS_ONCE() to READ_ONCE()/WRITE_ONCE()
    Commit-ID:  eeafcc5a5925d0819dad462eac1d42fda5fbe36f
    Gitweb: https://git.kernel.org/tip/eeafcc5a5925d0819dad462eac1d42fda5fbe36f
    Author: Mark Rutland <mark.rutland@arm.com>
    AuthorDate: Mon, 23 Oct 2017 14:07:13 -0700
    Committer: Ingo Molnar <mingo@kernel.org>
    CommitDate: Wed, 25 Oct 2017 11:00:57 +0200

    locking/atomics, firmware/ivc: Convert ACCESS_ONCE() to READ_ONCE()/WRITE_ONCE()

    workqueue: kill off ACCESS_ONCE()

    For several reasons, it is desirable to use {READ,WRITE}_ONCE() in
    preference to ACCESS_ONCE(), and new code is expected to use one of the
    former. So far, there's been no reason to change most existing uses of
    ACCESS_ONCE(), as these aren't currently harmful.

    However, for some features it is necessary to instrument reads and
    writes separately, which is not possible with ACCESS_ONCE(). This
    distinction is critical to correct operation.

    It's possible to transform the bulk of kernel code using the Coccinelle
    script below. However, this doesn't handle comments, leaving references
    to ACCESS_ONCE() instances which have been removed. As a preparatory
    step, this patch converts the Tegra IVC code and comments to use
    {READ,WRITE}_ONCE() consistently.

    ----
    virtual patch

    @ depends on patch @
    expression E1, E2;
    @@

    - ACCESS_ONCE(E1) = E2
    + WRITE_ONCE(E1, E2)

    @ depends on patch @
    expression E;
    @@

    - ACCESS_ONCE(E)
    + READ_ONCE(E)
    ----

    Signed-off-by: Mark Rutland <mark.rutland@arm.com>
    Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
    Cc: Jonathan Hunter <jonathanh@nvidia.com>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Thierry Reding <thierry.reding@gmail.com>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Cc: davem@davemloft.net
    Cc: linux-arch@vger.kernel.org
    Cc: mpe@ellerman.id.au
    Cc: shuah@kernel.org
    Cc: snitzer@redhat.com
    Cc: thor.thayer@linux.intel.com
    Cc: tj@kernel.org
    Cc: viro@zeniv.linux.org.uk
    Cc: will.deacon@arm.com
    Link: http://lkml.kernel.org/r/1508792849-3115-3-git-send-email-paulmck@linux.vnet.ibm.com
    Signed-off-by: Ingo Molnar <mingo@kernel.org>
    ---
    drivers/firmware/tegra/ivc.c | 24 ++++++++++++------------
    1 file changed, 12 insertions(+), 12 deletions(-)

    diff --git a/drivers/firmware/tegra/ivc.c b/drivers/firmware/tegra/ivc.c
    index a01461d..00de793 100644
    --- a/drivers/firmware/tegra/ivc.c
    +++ b/drivers/firmware/tegra/ivc.c
    @@ -99,11 +99,11 @@ static inline bool tegra_ivc_empty(struct tegra_ivc *ivc,
    {
    /*
    * This function performs multiple checks on the same values with
    - * security implications, so create snapshots with ACCESS_ONCE() to
    + * security implications, so create snapshots with READ_ONCE() to
    * ensure that these checks use the same values.
    */
    - u32 tx = ACCESS_ONCE(header->tx.count);
    - u32 rx = ACCESS_ONCE(header->rx.count);
    + u32 tx = READ_ONCE(header->tx.count);
    + u32 rx = READ_ONCE(header->rx.count);

    /*
    * Perform an over-full check to prevent denial of service attacks
    @@ -124,8 +124,8 @@ static inline bool tegra_ivc_empty(struct tegra_ivc *ivc,
    static inline bool tegra_ivc_full(struct tegra_ivc *ivc,
    struct tegra_ivc_header *header)
    {
    - u32 tx = ACCESS_ONCE(header->tx.count);
    - u32 rx = ACCESS_ONCE(header->rx.count);
    + u32 tx = READ_ONCE(header->tx.count);
    + u32 rx = READ_ONCE(header->rx.count);

    /*
    * Invalid cases where the counters indicate that the queue is over
    @@ -137,8 +137,8 @@ static inline bool tegra_ivc_full(struct tegra_ivc *ivc,
    static inline u32 tegra_ivc_available(struct tegra_ivc *ivc,
    struct tegra_ivc_header *header)
    {
    - u32 tx = ACCESS_ONCE(header->tx.count);
    - u32 rx = ACCESS_ONCE(header->rx.count);
    + u32 tx = READ_ONCE(header->tx.count);
    + u32 rx = READ_ONCE(header->rx.count);

    /*
    * This function isn't expected to be used in scenarios where an
    @@ -151,8 +151,8 @@ static inline u32 tegra_ivc_available(struct tegra_ivc *ivc,

    static inline void tegra_ivc_advance_tx(struct tegra_ivc *ivc)
    {
    - ACCESS_ONCE(ivc->tx.channel->tx.count) =
    - ACCESS_ONCE(ivc->tx.channel->tx.count) + 1;
    + WRITE_ONCE(ivc->tx.channel->tx.count,
    + READ_ONCE(ivc->tx.channel->tx.count) + 1);

    if (ivc->tx.position == ivc->num_frames - 1)
    ivc->tx.position = 0;
    @@ -162,8 +162,8 @@ static inline void tegra_ivc_advance_tx(struct tegra_ivc *ivc)

    static inline void tegra_ivc_advance_rx(struct tegra_ivc *ivc)
    {
    - ACCESS_ONCE(ivc->rx.channel->rx.count) =
    - ACCESS_ONCE(ivc->rx.channel->rx.count) + 1;
    + WRITE_ONCE(ivc->rx.channel->rx.count,
    + READ_ONCE(ivc->rx.channel->rx.count) + 1);

    if (ivc->rx.position == ivc->num_frames - 1)
    ivc->rx.position = 0;
    @@ -428,7 +428,7 @@ int tegra_ivc_notified(struct tegra_ivc *ivc)

    /* Copy the receiver's state out of shared memory. */
    tegra_ivc_invalidate(ivc, ivc->rx.phys + offset);
    - state = ACCESS_ONCE(ivc->rx.channel->tx.state);
    + state = READ_ONCE(ivc->rx.channel->tx.state);

    if (state == TEGRA_IVC_STATE_SYNC) {
    offset = offsetof(struct tegra_ivc_header, tx.count);
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