Commit 2a4fd070ee8561d918a3776388331bb7e92ea59e
1 parent
db61367038
Exists in
smarc-imx_3.14.28_1.0.0_ga
and in
1 other branch
blkcg: move bulk of blkcg_gq release operations to the RCU callback
Currently, when the last reference of a blkcg_gq is put, all then release operations sans the actual freeing happen directly in blkg_put(). As blkg_put() may be called under queue_lock, all pd_exit_fn()s may be too. This makes it impossible for pd_exit_fn()s to use del_timer_sync() on timers which grab the queue_lock which is an irq-safe lock due to the deadlock possibility described in the comment on top of del_timer_sync(). This can be easily avoided by perfoming the release operations in the RCU callback instead of directly from blkg_put(). This patch moves the blkcg_gq release operations to the RCU callback. As this leaves __blkg_release() with only call_rcu() invocation, blkg_rcu_free() is renamed to __blkg_release_rcu(), exported and call_rcu() invocation is now done directly from blkg_put() instead of going through __blkg_release() which is removed. Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: Vivek Goyal <vgoyal@redhat.com>
Showing 2 changed files with 18 additions and 20 deletions Side-by-side Diff
block/blk-cgroup.c
| ... | ... | @@ -369,13 +369,17 @@ |
| 369 | 369 | q->root_rl.blkg = NULL; |
| 370 | 370 | } |
| 371 | 371 | |
| 372 | -static void blkg_rcu_free(struct rcu_head *rcu_head) | |
| 372 | +/* | |
| 373 | + * A group is RCU protected, but having an rcu lock does not mean that one | |
| 374 | + * can access all the fields of blkg and assume these are valid. For | |
| 375 | + * example, don't try to follow throtl_data and request queue links. | |
| 376 | + * | |
| 377 | + * Having a reference to blkg under an rcu allows accesses to only values | |
| 378 | + * local to groups like group stats and group rate limits. | |
| 379 | + */ | |
| 380 | +void __blkg_release_rcu(struct rcu_head *rcu_head) | |
| 373 | 381 | { |
| 374 | - blkg_free(container_of(rcu_head, struct blkcg_gq, rcu_head)); | |
| 375 | -} | |
| 376 | - | |
| 377 | -void __blkg_release(struct blkcg_gq *blkg) | |
| 378 | -{ | |
| 382 | + struct blkcg_gq *blkg = container_of(rcu_head, struct blkcg_gq, rcu_head); | |
| 379 | 383 | int i; |
| 380 | 384 | |
| 381 | 385 | /* tell policies that this one is being freed */ |
| 382 | 386 | |
| 383 | 387 | |
| 384 | 388 | |
| ... | ... | @@ -388,21 +392,15 @@ |
| 388 | 392 | |
| 389 | 393 | /* release the blkcg and parent blkg refs this blkg has been holding */ |
| 390 | 394 | css_put(&blkg->blkcg->css); |
| 391 | - if (blkg->parent) | |
| 395 | + if (blkg->parent) { | |
| 396 | + spin_lock_irq(blkg->q->queue_lock); | |
| 392 | 397 | blkg_put(blkg->parent); |
| 398 | + spin_unlock_irq(blkg->q->queue_lock); | |
| 399 | + } | |
| 393 | 400 | |
| 394 | - /* | |
| 395 | - * A group is freed in rcu manner. But having an rcu lock does not | |
| 396 | - * mean that one can access all the fields of blkg and assume these | |
| 397 | - * are valid. For example, don't try to follow throtl_data and | |
| 398 | - * request queue links. | |
| 399 | - * | |
| 400 | - * Having a reference to blkg under an rcu allows acess to only | |
| 401 | - * values local to groups like group stats and group rate limits | |
| 402 | - */ | |
| 403 | - call_rcu(&blkg->rcu_head, blkg_rcu_free); | |
| 401 | + blkg_free(blkg); | |
| 404 | 402 | } |
| 405 | -EXPORT_SYMBOL_GPL(__blkg_release); | |
| 403 | +EXPORT_SYMBOL_GPL(__blkg_release_rcu); | |
| 406 | 404 | |
| 407 | 405 | /* |
| 408 | 406 | * The next function used by blk_queue_for_each_rl(). It's a bit tricky |
block/blk-cgroup.h
| ... | ... | @@ -266,7 +266,7 @@ |
| 266 | 266 | blkg->refcnt++; |
| 267 | 267 | } |
| 268 | 268 | |
| 269 | -void __blkg_release(struct blkcg_gq *blkg); | |
| 269 | +void __blkg_release_rcu(struct rcu_head *rcu); | |
| 270 | 270 | |
| 271 | 271 | /** |
| 272 | 272 | * blkg_put - put a blkg reference |
| ... | ... | @@ -279,7 +279,7 @@ |
| 279 | 279 | lockdep_assert_held(blkg->q->queue_lock); |
| 280 | 280 | WARN_ON_ONCE(blkg->refcnt <= 0); |
| 281 | 281 | if (!--blkg->refcnt) |
| 282 | - __blkg_release(blkg); | |
| 282 | + call_rcu(&blkg->rcu_head, __blkg_release_rcu); | |
| 283 | 283 | } |
| 284 | 284 | |
| 285 | 285 | struct blkcg_gq *__blkg_lookup(struct blkcg *blkcg, struct request_queue *q, |