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[98.128.181.28]) by smtp.gmail.com with ESMTPSA id a25sm1314400ljk.35.2021.02.12.05.16.15 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 12 Feb 2021 05:16:16 -0800 (PST) From: Ulf Hansson To: linux-mmc@vger.kernel.org, Ulf Hansson Cc: Adrian Hunter , Linus Walleij , Wolfram Sang , Pierre Ossman , Russell King , linux-kernel@vger.kernel.org Subject: [PATCH 2/2] mmc: core: Drop reference counting of the bus_ops Date: Fri, 12 Feb 2021 14:16:10 +0100 Message-Id: <20210212131610.236843-1-ulf.hansson@linaro.org> X-Mailer: git-send-email 2.25.1 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org When the mmc_rescan work is enabled for execution (host->rescan_disable), it's the only instance per mmc host that is allowed to set/clear the host->bus_ops pointer. Besides the mmc_rescan work, there are a couple of scenarios when the host->bus_ops pointer may be accessed. Typically, those can be described as as below: *) Upper mmc driver layers (like the mmc block device driver or an SDIO functional driver) needs to execute a host->bus_ops callback. This can be considered as safe without having to use some special locking mechanism, because they operate on top of the struct mmc_card. As long as there is a card to operate upon, the mmc core guarantees that there is a host->bus_ops assigned as well. Note that, upper layer mmc drivers are of course responsible to clean up from themselves from their ->remove() callbacks, otherwise things would fall apart anyways. **) Via the mmc host instance, we may need to force a removal of an inserted mmc card. This happens when a mmc host driver gets unbind, for example. In this case, we protect the host->bus_ops pointer from concurrent accesses, by disabling the mmc_rescan work upfront (host->rescan_disable). See mmc_stop_host() for example. This said, it seems like the reference counting of the host->bus_ops pointer at some point have become superfluous. As this is an old mechanism of the mmc core, it a bit difficult to digest the history of when that could have happened. However, let's drop the reference counting to avoid unnecessary code-paths and lockings. Cc: Pierre Ossman Cc: Russell King Signed-off-by: Ulf Hansson --- drivers/mmc/core/core.c | 89 ++-------------------------------------- include/linux/mmc/host.h | 2 - 2 files changed, 4 insertions(+), 87 deletions(-) diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c index 2e41fa598bd6..860995eb548b 100644 --- a/drivers/mmc/core/core.c +++ b/drivers/mmc/core/core.c @@ -1377,63 +1377,13 @@ void mmc_power_cycle(struct mmc_host *host, u32 ocr) mmc_power_up(host, ocr); } -/* - * Cleanup when the last reference to the bus operator is dropped. - */ -static void __mmc_release_bus(struct mmc_host *host) -{ - WARN_ON(!host->bus_dead); - - host->bus_ops = NULL; -} - -/* - * Increase reference count of bus operator - */ -static inline void mmc_bus_get(struct mmc_host *host) -{ - unsigned long flags; - - spin_lock_irqsave(&host->lock, flags); - host->bus_refs++; - spin_unlock_irqrestore(&host->lock, flags); -} - -/* - * Decrease reference count of bus operator and free it if - * it is the last reference. - */ -static inline void mmc_bus_put(struct mmc_host *host) -{ - unsigned long flags; - - spin_lock_irqsave(&host->lock, flags); - host->bus_refs--; - if ((host->bus_refs == 0) && host->bus_ops) - __mmc_release_bus(host); - spin_unlock_irqrestore(&host->lock, flags); -} - /* * Assign a mmc bus handler to a host. Only one bus handler may control a * host at any given time. */ void mmc_attach_bus(struct mmc_host *host, const struct mmc_bus_ops *ops) { - unsigned long flags; - - WARN_ON(!host->claimed); - - spin_lock_irqsave(&host->lock, flags); - - WARN_ON(host->bus_ops); - WARN_ON(host->bus_refs); - host->bus_ops = ops; - host->bus_refs = 1; - host->bus_dead = 0; - - spin_unlock_irqrestore(&host->lock, flags); } /* @@ -1441,18 +1391,7 @@ void mmc_attach_bus(struct mmc_host *host, const struct mmc_bus_ops *ops) */ void mmc_detach_bus(struct mmc_host *host) { - unsigned long flags; - - WARN_ON(!host->claimed); - WARN_ON(!host->bus_ops); - - spin_lock_irqsave(&host->lock, flags); - - host->bus_dead = 1; - - spin_unlock_irqrestore(&host->lock, flags); - - mmc_bus_put(host); + host->bus_ops = NULL; } void _mmc_detect_change(struct mmc_host *host, unsigned long delay, bool cd_irq) @@ -2244,32 +2183,15 @@ void mmc_rescan(struct work_struct *work) host->trigger_card_event = false; } - mmc_bus_get(host); - /* Verify a registered card to be functional, else remove it. */ - if (host->bus_ops && !host->bus_dead) + if (host->bus_ops) host->bus_ops->detect(host); host->detect_change = 0; - /* - * Let mmc_bus_put() free the bus/bus_ops if we've found that - * the card is no longer present. - */ - mmc_bus_put(host); - mmc_bus_get(host); - /* if there still is a card present, stop here */ - if (host->bus_ops != NULL) { - mmc_bus_put(host); + if (host->bus_ops != NULL) goto out; - } - - /* - * Only we can add a new handler, so it's safe to - * release the lock here. - */ - mmc_bus_put(host); mmc_claim_host(host); if (mmc_card_is_removable(host) && host->ops->get_cd && @@ -2332,18 +2254,15 @@ void mmc_stop_host(struct mmc_host *host) /* clear pm flags now and let card drivers set them as needed */ host->pm_flags = 0; - mmc_bus_get(host); - if (host->bus_ops && !host->bus_dead) { + if (host->bus_ops) { /* Calling bus_ops->remove() with a claimed host can deadlock */ host->bus_ops->remove(host); mmc_claim_host(host); mmc_detach_bus(host); mmc_power_off(host); mmc_release_host(host); - mmc_bus_put(host); return; } - mmc_bus_put(host); mmc_claim_host(host); mmc_power_off(host); diff --git a/include/linux/mmc/host.h b/include/linux/mmc/host.h index 927ba7566617..7b5555c705fd 100644 --- a/include/linux/mmc/host.h +++ b/include/linux/mmc/host.h @@ -423,7 +423,6 @@ struct mmc_host { /* group bitfields together to minimize padding */ unsigned int use_spi_crc:1; unsigned int claimed:1; /* host exclusively claimed */ - unsigned int bus_dead:1; /* bus has been released */ unsigned int doing_init_tune:1; /* initial tuning in progress */ unsigned int can_retune:1; /* re-tuning can be used */ unsigned int doing_retune:1; /* re-tuning in progress */ @@ -455,7 +454,6 @@ struct mmc_host { struct mmc_slot slot; const struct mmc_bus_ops *bus_ops; /* current bus driver */ - unsigned int bus_refs; /* reference counter */ unsigned int sdio_irqs; struct task_struct *sdio_irq_thread; -- 2.25.1