From: Alex Smith Date: Tue, 6 Oct 2015 13:52:07 +0000 (+0100) Subject: mtd: nand: increase ready wait timeout and report timeouts X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=b70af9bef49b;p=linux-beck.git mtd: nand: increase ready wait timeout and report timeouts If nand_wait_ready() times out, this is silently ignored, and its caller will then proceed to read from/write to the chip before it is ready. This can potentially result in corruption with no indication as to why. While a 20ms timeout seems like it should be plenty enough, certain behaviour can cause it to timeout much earlier than expected. The situation which prompted this change was that CPU 0, which is responsible for updating jiffies, was holding interrupts disabled for a fairly long time while writing to the console during a printk, causing several jiffies updates to be delayed. If CPU 1 happens to enter the timeout loop in nand_wait_ready() just before CPU 0 re- enables interrupts and updates jiffies, CPU 1 will immediately time out when the delayed jiffies updates are made. The result of this is that nand_wait_ready() actually waits less time than the NAND chip would normally take to be ready, and then read_page() proceeds to read out bad data from the chip. The situation described above may seem unlikely, but in fact it can be reproduced almost every boot on the MIPS Creator Ci20. Therefore, this patch increases the timeout to 400ms. This should be enough to cover cases where jiffies updates get delayed. In nand_wait() the timeout was previously chosen based on whether erasing or programming. This is changed to be 400ms unconditionally as well to avoid similar problems there. nand_wait() is also slightly refactored to be consistent with nand_wait{,_status}_ready(). These changes should have no effect during normal operation. Debugging this was made more difficult by the misleading comment above nand_wait_ready() stating "The timeout is caught later" - no timeout was ever reported, leading me away from the real source of the problem. Therefore, a pr_warn() is added when a timeout does occur so that it is easier to pinpoint similar problems in future. Signed-off-by: Alex Smith Signed-off-by: Harvey Hunt Reviewed-by: Niklas Cassel Cc: Alex Smith Cc: Zubair Lutfullah Kakakhel Cc: David Woodhouse Cc: Niklas Cassel Signed-off-by: Brian Norris --- diff --git a/drivers/mtd/nand/nand_base.c b/drivers/mtd/nand/nand_base.c index d87c7d0b4675..cc74142938b0 100644 --- a/drivers/mtd/nand/nand_base.c +++ b/drivers/mtd/nand/nand_base.c @@ -543,23 +543,32 @@ static void panic_nand_wait_ready(struct mtd_info *mtd, unsigned long timeo) } } -/* Wait for the ready pin, after a command. The timeout is caught later. */ +/** + * nand_wait_ready - [GENERIC] Wait for the ready pin after commands. + * @mtd: MTD device structure + * + * Wait for the ready pin after a command, and warn if a timeout occurs. + */ void nand_wait_ready(struct mtd_info *mtd) { struct nand_chip *chip = mtd->priv; - unsigned long timeo = jiffies + msecs_to_jiffies(20); + unsigned long timeo = 400; - /* 400ms timeout */ if (in_interrupt() || oops_in_progress) - return panic_nand_wait_ready(mtd, 400); + return panic_nand_wait_ready(mtd, timeo); led_trigger_event(nand_led_trigger, LED_FULL); /* Wait until command is processed or timeout occurs */ + timeo = jiffies + msecs_to_jiffies(timeo); do { if (chip->dev_ready(mtd)) - break; - touch_softlockup_watchdog(); + goto out; + cond_resched(); } while (time_before(jiffies, timeo)); + + pr_warn_ratelimited( + "timeout while waiting for chip to become ready\n"); +out: led_trigger_event(nand_led_trigger, LED_OFF); } EXPORT_SYMBOL_GPL(nand_wait_ready); @@ -885,15 +894,13 @@ static void panic_nand_wait(struct mtd_info *mtd, struct nand_chip *chip, * @mtd: MTD device structure * @chip: NAND chip structure * - * Wait for command done. This applies to erase and program only. Erase can - * take up to 400ms and program up to 20ms according to general NAND and - * SmartMedia specs. + * Wait for command done. This applies to erase and program only. */ static int nand_wait(struct mtd_info *mtd, struct nand_chip *chip) { - int status, state = chip->state; - unsigned long timeo = (state == FL_ERASING ? 400 : 20); + int status; + unsigned long timeo = 400; led_trigger_event(nand_led_trigger, LED_FULL); @@ -909,7 +916,7 @@ static int nand_wait(struct mtd_info *mtd, struct nand_chip *chip) panic_nand_wait(mtd, chip, timeo); else { timeo = jiffies + msecs_to_jiffies(timeo); - while (time_before(jiffies, timeo)) { + do { if (chip->dev_ready) { if (chip->dev_ready(mtd)) break; @@ -918,7 +925,7 @@ static int nand_wait(struct mtd_info *mtd, struct nand_chip *chip) break; } cond_resched(); - } + } while (time_before(jiffies, timeo)); } led_trigger_event(nand_led_trigger, LED_OFF);