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    SubjectRe: [PATCH 3/4] firewire: enforce access order between generation and node ID
    Stefan Richter wrote:
    > I'm going to commit it with a whitespace adjustment and a comment typo
    > fixed.

    Also forgot to #include <asm/system.h> in some of the files. Here is
    the final product, for the record.


    From: Stefan Richter <stefanr@s5r6.in-berlin.de>
    Subject: firewire: enforce access order between generation and node ID, fix "giving up on config rom"

    fw_device.node_id and fw_device.generation are accessed without mutexes.
    We have to ensure that all readers will get to see node_id updates
    before generation updates.

    Fixes an inability to recognize devices after "giving up on config rom",
    https://bugzilla.redhat.com/show_bug.cgi?id=429950

    Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>

    Reviewed by Nick Piggin <nickpiggin@yahoo.com.au>.

    Verified to fix 'giving up on config rom' issues on multiple system and
    drive combinations that were previously affected.

    Signed-off-by: Jarod Wilson <jwilson@redhat.com>
    ---
    drivers/firewire/fw-cdev.c | 1 +
    drivers/firewire/fw-device.c | 15 +++++++++++++--
    drivers/firewire/fw-device.h | 12 ++++++++++++
    drivers/firewire/fw-sbp2.c | 3 +++
    drivers/firewire/fw-topology.c | 6 ++++++
    5 files changed, 35 insertions(+), 2 deletions(-)

    Index: linux/drivers/firewire/fw-device.c
    ===================================================================
    --- linux.orig/drivers/firewire/fw-device.c
    +++ linux/drivers/firewire/fw-device.c
    @@ -27,6 +27,7 @@
    #include <linux/idr.h>
    #include <linux/rwsem.h>
    #include <asm/semaphore.h>
    +#include <asm/system.h>
    #include <linux/ctype.h>
    #include "fw-transaction.h"
    #include "fw-topology.h"
    @@ -182,9 +183,14 @@ static void fw_device_release(struct dev

    int fw_device_enable_phys_dma(struct fw_device *device)
    {
    + int generation = device->generation;
    +
    + /* device->node_id, accessed below, must not be older than generation */
    + smp_rmb();
    +
    return device->card->driver->enable_phys_dma(device->card,
    device->node_id,
    - device->generation);
    + generation);
    }
    EXPORT_SYMBOL(fw_device_enable_phys_dma);

    @@ -389,12 +395,16 @@ static int read_rom(struct fw_device *de
    struct read_quadlet_callback_data callback_data;
    struct fw_transaction t;
    u64 offset;
    + int generation = device->generation;
    +
    + /* device->node_id, accessed below, must not be older than generation */
    + smp_rmb();

    init_completion(&callback_data.done);

    offset = 0xfffff0000400ULL + index * 4;
    fw_send_request(device->card, &t, TCODE_READ_QUADLET_REQUEST,
    - device->node_id, device->generation, device->max_speed,
    + device->node_id, generation, device->max_speed,
    offset, NULL, 4, complete_transaction, &callback_data);

    wait_for_completion(&callback_data.done);
    @@ -801,6 +811,7 @@ void fw_node_event(struct fw_card *card,

    device = node->data;
    device->node_id = node->node_id;
    + smp_wmb(); /* update node_id before generation */
    device->generation = card->generation;
    if (atomic_read(&device->state) == FW_DEVICE_RUNNING) {
    PREPARE_DELAYED_WORK(&device->work, fw_device_update);
    Index: linux/drivers/firewire/fw-topology.c
    ===================================================================
    --- linux.orig/drivers/firewire/fw-topology.c
    +++ linux/drivers/firewire/fw-topology.c
    @@ -21,6 +21,7 @@
    #include <linux/module.h>
    #include <linux/wait.h>
    #include <linux/errno.h>
    +#include <asm/system.h>
    #include "fw-transaction.h"
    #include "fw-topology.h"

    @@ -518,6 +519,11 @@ fw_core_handle_bus_reset(struct fw_card
    card->bm_retries = 0;

    card->node_id = node_id;
    + /*
    + * Update node_id before generation to prevent anybody from using
    + * a stale node_id together with a current generation.
    + */
    + smp_wmb();
    card->generation = generation;
    card->reset_jiffies = jiffies;
    schedule_delayed_work(&card->work, 0);
    Index: linux/drivers/firewire/fw-sbp2.c
    ===================================================================
    --- linux.orig/drivers/firewire/fw-sbp2.c
    +++ linux/drivers/firewire/fw-sbp2.c
    @@ -40,6 +40,7 @@
    #include <linux/stringify.h>
    #include <linux/timer.h>
    #include <linux/workqueue.h>
    +#include <asm/system.h>

    #include <scsi/scsi.h>
    #include <scsi/scsi_cmnd.h>
    @@ -662,6 +663,7 @@ static void sbp2_login(struct work_struc
    int generation, node_id, local_node_id;

    generation = device->generation;
    + smp_rmb(); /* node_id must not be older than generation */
    node_id = device->node_id;
    local_node_id = device->card->node_id;

    @@ -912,6 +914,7 @@ static void sbp2_reconnect(struct work_s
    int generation, node_id, local_node_id;

    generation = device->generation;
    + smp_rmb(); /* node_id must not be older than generation */
    node_id = device->node_id;
    local_node_id = device->card->node_id;

    Index: linux/drivers/firewire/fw-device.h
    ===================================================================
    --- linux.orig/drivers/firewire/fw-device.h
    +++ linux/drivers/firewire/fw-device.h
    @@ -35,6 +35,18 @@ struct fw_attribute_group {
    struct attribute *attrs[11];
    };

    +/*
    + * Note, fw_device.generation always has to be read before fw_device.node_id.
    + * Use SMP memory barriers to ensure this. Otherwise requests will be sent
    + * to an outdated node_id if the generation was updated in the meantime due
    + * to a bus reset.
    + *
    + * Likewise, fw-core will take care to update .node_id before .generation so
    + * that whenever fw_device.generation is current WRT the actual bus generation,
    + * fw_device.node_id is guaranteed to be current too.
    + *
    + * The same applies to fw_device.card->node_id vs. fw_device.generation.
    + */
    struct fw_device {
    atomic_t state;
    struct fw_node *node;
    Index: linux/drivers/firewire/fw-cdev.c
    ===================================================================
    --- linux.orig/drivers/firewire/fw-cdev.c
    +++ linux/drivers/firewire/fw-cdev.c
    @@ -207,6 +207,7 @@ fill_bus_reset_event(struct fw_cdev_even
    event->closure = client->bus_reset_closure;
    event->type = FW_CDEV_EVENT_BUS_RESET;
    event->generation = client->device->generation;
    + smp_rmb(); /* node_id must not be older than generation */
    event->node_id = client->device->node_id;
    event->local_node_id = card->local_node->node_id;
    event->bm_node_id = 0; /* FIXME: We don't track the BM. */
    --
    Stefan Richter
    -=====-==--- ---= ==--=
    http://arcgraph.de/sr/


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