| Message ID | 20170712042304.19745-3-cyrilbur@gmail.com |
|---|---|
| State | Superseded |
| Headers | show |
On Wed, 2017-07-12 at 14:22 +1000, Cyril Bur wrote: > OPAL can only manage one flash access at a time and will return an > OPAL_BUSY error for each concurrent access to the flash. The simplest > way to prevent this from happening is with a mutex. > > Signed-off-by: Cyril Bur <cyrilbur@gmail.com> > --- Should the mutex_lock() be mutex_lock_interruptible()? Are we OK waiting on the mutex while other operations with the lock are busy? Balbir Singh.
On Mon, 2017-07-17 at 17:34 +1000, Balbir Singh wrote: > On Wed, 2017-07-12 at 14:22 +1000, Cyril Bur wrote: > > OPAL can only manage one flash access at a time and will return an > > OPAL_BUSY error for each concurrent access to the flash. The simplest > > way to prevent this from happening is with a mutex. > > > > Signed-off-by: Cyril Bur <cyrilbur@gmail.com> > > --- > > Should the mutex_lock() be mutex_lock_interruptible()? Are we OK waiting on > the mutex while other operations with the lock are busy? > This is a good question. My best interpretation is that _interruptible() should be used when you'll only be coming from a user context. Which is mostly true for this driver, however, MTD does provide kernel interfaces, so I was hesitant, there isn't a great deal of use of _interruptible() in drivers/mtd. Thoughts? Cyril > Balbir Singh. >
On Mon, 2017-07-17 at 17:55 +1000, Cyril Bur wrote: > On Mon, 2017-07-17 at 17:34 +1000, Balbir Singh wrote: > > On Wed, 2017-07-12 at 14:22 +1000, Cyril Bur wrote: > > > OPAL can only manage one flash access at a time and will return an > > > OPAL_BUSY error for each concurrent access to the flash. The simplest > > > way to prevent this from happening is with a mutex. > > > > > > Signed-off-by: Cyril Bur <cyrilbur@gmail.com> > > > --- > > > > Should the mutex_lock() be mutex_lock_interruptible()? Are we OK waiting on > > the mutex while other operations with the lock are busy? > > > > This is a good question. My best interpretation is that > _interruptible() should be used when you'll only be coming from a user > context. Which is mostly true for this driver, however, MTD does > provide kernel interfaces, so I was hesitant, there isn't a great deal > of use of _interruptible() in drivers/mtd. > > Thoughts? What are the kernel interfaces (I have not read through mtd in detail)? I would still like to see us not blocked in mutex_lock() across threads for parallel calls, one option is to use mutex_trylock() and return if someone already holds the mutex with -EBUSY, but you'll need to evaluate what that means for every call. Balbir Singh.
On Mon, 2017-07-17 at 19:29 +1000, Balbir Singh wrote: > On Mon, 2017-07-17 at 17:55 +1000, Cyril Bur wrote: > > On Mon, 2017-07-17 at 17:34 +1000, Balbir Singh wrote: > > > On Wed, 2017-07-12 at 14:22 +1000, Cyril Bur wrote: > > > > OPAL can only manage one flash access at a time and will return an > > > > OPAL_BUSY error for each concurrent access to the flash. The simplest > > > > way to prevent this from happening is with a mutex. > > > > > > > > Signed-off-by: Cyril Bur <cyrilbur@gmail.com> > > > > --- > > > > > > Should the mutex_lock() be mutex_lock_interruptible()? Are we OK waiting on > > > the mutex while other operations with the lock are busy? > > > > > > > This is a good question. My best interpretation is that > > _interruptible() should be used when you'll only be coming from a user > > context. Which is mostly true for this driver, however, MTD does > > provide kernel interfaces, so I was hesitant, there isn't a great deal > > of use of _interruptible() in drivers/mtd. > > > > Thoughts? > > What are the kernel interfaces (I have not read through mtd in detail)? > I would still like to see us not blocked in mutex_lock() across threads > for parallel calls, one option is to use mutex_trylock() and return if > someone already holds the mutex with -EBUSY, but you'll need to evaluate > what that means for every call. > Yeah maybe mutex_trylock() is the way to go, thinking quickly, I don't see how it could be a problem for userspace using powernv_flash. I'm honestly not too sure about the depths of the mtd kernel interfaces but I've seen a tonne of cool stuff you could do, hence my reluctance to go with _interruptible() Cyril > Balbir Singh. >
Cyril Bur <cyrilbur@gmail.com> writes: > On Mon, 2017-07-17 at 19:29 +1000, Balbir Singh wrote: >> On Mon, 2017-07-17 at 17:55 +1000, Cyril Bur wrote: >> > On Mon, 2017-07-17 at 17:34 +1000, Balbir Singh wrote: >> > > On Wed, 2017-07-12 at 14:22 +1000, Cyril Bur wrote: >> > > > OPAL can only manage one flash access at a time and will return an >> > > > OPAL_BUSY error for each concurrent access to the flash. The simplest >> > > > way to prevent this from happening is with a mutex. >> > > > >> > > > Signed-off-by: Cyril Bur <cyrilbur@gmail.com> >> > > > --- >> > > >> > > Should the mutex_lock() be mutex_lock_interruptible()? Are we OK waiting on >> > > the mutex while other operations with the lock are busy? >> > > >> > >> > This is a good question. My best interpretation is that >> > _interruptible() should be used when you'll only be coming from a user >> > context. Which is mostly true for this driver, however, MTD does >> > provide kernel interfaces, so I was hesitant, there isn't a great deal >> > of use of _interruptible() in drivers/mtd. >> > >> > Thoughts? >> >> What are the kernel interfaces (I have not read through mtd in detail)? >> I would still like to see us not blocked in mutex_lock() across threads >> for parallel calls, one option is to use mutex_trylock() and return if >> someone already holds the mutex with -EBUSY, but you'll need to evaluate >> what that means for every call. > > Yeah maybe mutex_trylock() is the way to go, thinking quickly, I don't > see how it could be a problem for userspace using powernv_flash. I'm > honestly not too sure about the depths of the mtd kernel interfaces but > I've seen a tonne of cool stuff you could do, hence my reluctance to go > with _interruptible() If you use trylock that means all your callers now need to handle EBUSY, which I doubt they do. Which means it goes up to userspace, which most users will just treat as a hard error. So that sounds like a bad plan to me. cheers
diff --git a/drivers/mtd/devices/powernv_flash.c b/drivers/mtd/devices/powernv_flash.c index a9a20c00687c..7b41af06f4fe 100644 --- a/drivers/mtd/devices/powernv_flash.c +++ b/drivers/mtd/devices/powernv_flash.c @@ -38,6 +38,7 @@ struct powernv_flash { struct mtd_info mtd; + struct mutex lock; u32 id; }; @@ -59,12 +60,15 @@ static int powernv_flash_async_op(struct mtd_info *mtd, enum flash_op op, dev_dbg(dev, "%s(op=%d, offset=0x%llx, len=%zu)\n", __func__, op, offset, len); + mutex_lock(&info->lock); + token = opal_async_get_token_interruptible(); if (token < 0) { if (token != -ERESTARTSYS) dev_err(dev, "Failed to get an async token\n"); - return token; + rc = token; + goto out; } switch (op) { @@ -79,18 +83,21 @@ static int powernv_flash_async_op(struct mtd_info *mtd, enum flash_op op, break; default: WARN_ON_ONCE(1); - return -EIO; + rc = -EIO; + goto out; } if (rc != OPAL_ASYNC_COMPLETION) { dev_err(dev, "opal_flash_async_op(op=%d) failed (rc %d)\n", op, rc); opal_async_release_token(token); - return -EIO; + rc = -EIO; + goto out; } rc = opal_async_wait_response(token, &msg); opal_async_release_token(token); + mutex_unlock(&info->lock); if (rc) { dev_err(dev, "opal async wait failed (rc %d)\n", rc); return -EIO; @@ -106,6 +113,9 @@ static int powernv_flash_async_op(struct mtd_info *mtd, enum flash_op op, } return rc; +out: + mutex_unlock(&info->lock); + return rc; } /** @@ -237,6 +247,8 @@ static int powernv_flash_probe(struct platform_device *pdev) if (ret) goto out; + mutex_init(&data->lock); + dev_set_drvdata(dev, data); /*
OPAL can only manage one flash access at a time and will return an OPAL_BUSY error for each concurrent access to the flash. The simplest way to prevent this from happening is with a mutex. Signed-off-by: Cyril Bur <cyrilbur@gmail.com> --- drivers/mtd/devices/powernv_flash.c | 18 +++++++++++++++--- 1 file changed, 15 insertions(+), 3 deletions(-)