Re: [PATCH v3 02/10] mtd: powernv_flash: Lock around concurrent access to OPAL
Cyril Bur 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 >> > > > --- >> > > >> > > 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
Re: [PATCH v3 02/10] mtd: powernv_flash: Lock around concurrent access to OPAL
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 > > > > --- > > > > > > 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. >
Re: [PATCH v3 02/10] mtd: powernv_flash: Lock around concurrent access to OPAL
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 > > > --- > > > > 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.
Re: [PATCH v3 02/10] mtd: powernv_flash: Lock around concurrent access to OPAL
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 > > --- > > 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. >
Re: [PATCH v3 02/10] mtd: powernv_flash: Lock around concurrent access to OPAL
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 > --- 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.
