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Message-ID: <20190614125940.GP3436@hirez.programming.kicks-ass.net>
Date: Fri, 14 Jun 2019 14:59:40 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Christian König
<ckoenig.leichtzumerken@...il.com>
Cc: daniel@...ll.ch, l.stach@...gutronix.de,
linux+etnaviv@...linux.org.uk, christian.gmeiner@...il.com,
yuq825@...il.com, eric@...olt.net, thellstrom@...are.com,
dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
etnaviv@...ts.freedesktop.org, lima@...ts.freedesktop.org
Subject: Re: [PATCH 3/6] drm/gem: use new ww_mutex_(un)lock_for_each macros
On Fri, Jun 14, 2019 at 02:41:22PM +0200, Christian König wrote:
> Use the provided macros instead of implementing deadlock handling on our own.
>
> Signed-off-by: Christian König <christian.koenig@....com>
> ---
> drivers/gpu/drm/drm_gem.c | 49 ++++++++++-----------------------------
> 1 file changed, 12 insertions(+), 37 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c
> index 50de138c89e0..6e4623d3bee2 100644
> --- a/drivers/gpu/drm/drm_gem.c
> +++ b/drivers/gpu/drm/drm_gem.c
> @@ -1307,51 +1307,26 @@ int
> drm_gem_lock_reservations(struct drm_gem_object **objs, int count,
> struct ww_acquire_ctx *acquire_ctx)
> {
> - int contended = -1;
> + struct ww_mutex *contended;
> int i, ret;
>
> ww_acquire_init(acquire_ctx, &reservation_ww_class);
>
> -retry:
> - if (contended != -1) {
> - struct drm_gem_object *obj = objs[contended];
> -
> - ret = ww_mutex_lock_slow_interruptible(&obj->resv->lock,
> - acquire_ctx);
> - if (ret) {
> - ww_acquire_done(acquire_ctx);
> - return ret;
> - }
> - }
> -
> - for (i = 0; i < count; i++) {
> - if (i == contended)
> - continue;
> -
> - ret = ww_mutex_lock_interruptible(&objs[i]->resv->lock,
> - acquire_ctx);
> - if (ret) {
> - int j;
> -
> - for (j = 0; j < i; j++)
> - ww_mutex_unlock(&objs[j]->resv->lock);
> -
> - if (contended != -1 && contended >= i)
> - ww_mutex_unlock(&objs[contended]->resv->lock);
> -
> - if (ret == -EDEADLK) {
> - contended = i;
> - goto retry;
retry here, starts the whole locking loop.
> - }
> -
> - ww_acquire_done(acquire_ctx);
> - return ret;
> - }
> - }
+#define ww_mutex_unlock_for_each(loop, pos, contended) \
+ if (!IS_ERR(contended)) { \
+ if (contended) \
+ ww_mutex_unlock(contended); \
+ contended = (pos); \
+ loop { \
+ if (contended == (pos)) \
+ break; \
+ ww_mutex_unlock(pos); \
+ } \
+ }
+
+#define ww_mutex_lock_for_each(loop, pos, contended, ret, intr, ctx) \
+ for (contended = ERR_PTR(-ENOENT); ({ \
+ __label__ relock, next; \
+ ret = -ENOENT; \
+ if (contended == ERR_PTR(-ENOENT)) \
+ contended = NULL; \
+ else if (contended == ERR_PTR(-EDEADLK)) \
+ contended = (pos); \
+ else \
+ goto next; \
+ loop { \
+ if (contended == (pos)) { \
+ contended = NULL; \
+ continue; \
+ } \
+relock: \
+ ret = !(intr) ? ww_mutex_lock(pos, ctx) : \
+ ww_mutex_lock_interruptible(pos, ctx); \
+ if (ret == -EDEADLK) { \
+ ww_mutex_unlock_for_each(loop, pos, \
+ contended); \
+ contended = ERR_PTR(-EDEADLK); \
+ goto relock; \
while relock here continues where it left of and doesn't restart @loop.
Or am I reading this monstrosity the wrong way?
+ } \
+ break; \
+next: \
+ continue; \
+ } \
+ }), ret != -ENOENT;)
+
> + ww_mutex_lock_for_each(for (i = 0; i < count; i++),
> + &objs[i]->resv->lock, contended, ret, true,
> + acquire_ctx)
> + if (ret)
> + goto error;
>
> ww_acquire_done(acquire_ctx);
>
> return 0;
> +
> +error:
> + ww_mutex_unlock_for_each(for (i = 0; i < count; i++),
> + &objs[i]->resv->lock, contended);
> + ww_acquire_done(acquire_ctx);
> + return ret;
> }
> EXPORT_SYMBOL(drm_gem_lock_reservations);
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