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firewire: cdev: use atomic_t for iso_resource_auto todo member

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The transition state of an iso_resource_auto client resource has no
effect on the client, so the client-level lock is not suitable for
protecting it.

At present, this state is the only member that requires mutual
exclusion. Adding a separate lock for it would be excessive.

Change the type of the transition state to atomic_t and use an atomic
compare-and-swap operation to preserve consistency.

Link: https://lore.kernel.org/r/20260927230724.119305-2-o-takashi@sakamocchi.jp
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
This commit is contained in:
Takashi Sakamoto 2026-09-28 08:07:23 +09:00
parent c94caec799
commit 2b69c5fe9e
1 changed files with 15 additions and 20 deletions
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35
drivers/firewire/core-cdev.c
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@ -133,16 +133,17 @@ struct iso_resource_params {
s32 bandwidth;
};
enum {
ISO_RES_AUTO_ALLOC,
ISO_RES_AUTO_REALLOC,
ISO_RES_AUTO_DEALLOC,
};
struct iso_resource_auto {
struct client_resource resource;
struct client *client;
/* Schedule work and access todo only with client->lock held. */
struct delayed_work work;
enum {
ISO_RES_AUTO_ALLOC,
ISO_RES_AUTO_REALLOC,
ISO_RES_AUTO_DEALLOC,
} todo;
atomic_t todo; // one of ISO_RES_AUTO_XXX.
int generation;
struct iso_resource_params params;
struct iso_resource_event *e_alloc, *e_dealloc;
@ -1338,16 +1339,14 @@ static void iso_resource_auto_work(struct work_struct *work)
struct iso_resource_auto *r = from_work(r, work, work.work);
struct client *client = r->client;
unsigned long index = r->resource.handle;
int channel, bandwidth, todo;
int channel, bandwidth;
bool free;
u64 reset_jiffies = client->device->card->reset_jiffies;
int current_generation = client->device->generation;
int resource_generation = xchg(&r->generation, current_generation); // But no need to be atomic.
scoped_guard(spinlock_irq, &client->lock)
todo = r->todo;
int todo = atomic_read(&r->todo);
switch (todo) {
case ISO_RES_AUTO_ALLOC:
@ -1404,12 +1403,10 @@ static void iso_resource_auto_work(struct work_struct *work)
// Notify the userspace client of the failure through a deallocation event.
e = xchg(&r->e_dealloc, NULL); // But no need to be atomic.
} else {
// Transit from allocation to reallocation, except if the client requested
// deallocation in the meantime.
scoped_guard(spinlock_irq, &client->lock) {
if (r->todo == ISO_RES_AUTO_ALLOC)
r->todo = ISO_RES_AUTO_REALLOC;
}
// Transit from allocation to reallocation. Use compare-and-swap atomic
// operation because the todo member can be set with ISO_RES_AUTO_DEALLOC
// by release_iso_resource_auto() in parallel.
atomic_cmpxchg_relaxed(&r->todo, ISO_RES_AUTO_ALLOC, ISO_RES_AUTO_REALLOC);
if (channel >= 0)
r->params.channels_mask = BIT_ULL(channel);
@ -1440,9 +1437,7 @@ static void release_iso_resource_auto(struct client *client, struct client_resou
{
struct iso_resource_auto *r = to_iso_resource_auto(resource);
guard(spinlock_irq)(&client->lock);
r->todo = ISO_RES_AUTO_DEALLOC;
atomic_set(&r->todo, ISO_RES_AUTO_DEALLOC);
schedule_iso_resource_auto(r, 0);
}
@ -1463,7 +1458,7 @@ static int ioctl_allocate_iso_resource(struct client *client, union ioctl_arg *a
INIT_DELAYED_WORK(&r->work, iso_resource_auto_work);
r->client = client;
r->todo = ISO_RES_AUTO_ALLOC;
atomic_set(&r->todo, ISO_RES_AUTO_ALLOC);
r->e_alloc = e1;
r->e_dealloc = e2;