Re: [PATCH tip/core/rcu 2/3] srcu: Force full grace-period ordering
On Mon, Jan 23, 2017 at 07:12:03PM +1100, Michael Ellerman wrote: > "Paul E. McKenney"writes: > > > On Sat, Jan 14, 2017 at 11:54:17AM -0800, Paul E. McKenney wrote: > >> On Sat, Jan 14, 2017 at 10:35:50AM +0100, Ingo Molnar wrote: > >> > * Paul E. McKenney wrote: > > > > [ . . . ] > > > >> > > + */ > >> > > +#ifdef CONFIG_PPC > >> > > +#define smp_mb__after_unlock_lock() smp_mb() /* Full ordering for > >> > > lock. */ > >> > > +#else /* #ifdef CONFIG_PPC */ > >> > > +#define smp_mb__after_unlock_lock() do { } while (0) > >> > > +#endif /* #else #ifdef CONFIG_PPC */ > >> > > >> > Yeah, so I realize that this was pre-existing code, but putting > >> > CONFIG_$ARCH > >> > #ifdefs into generic headers is generally frowned upon. > >> > > >> > The canonical approach would be either to define a helper Kconfig > >> > variable that > >> > can be set by PPC (but other architectures don't need to set it), or to > >> > expose a > >> > suitable macro (function) for architectures to define in their barrier.h > >> > arch > >> > header file. > >> > >> Very well, I will add a separate commit for this. 4.11 OK? > > > > Does the patch below seem reasonable? > > > > Thanx, Paul > > > > > > > > commit 271c0601237c41a279f975563e13837bace0df03 > > Author: Paul E. McKenney > > Date: Sat Jan 14 13:32:50 2017 -0800 > > > > rcu: Make arch select smp_mb__after_unlock_lock() strength > > > > The definition of smp_mb__after_unlock_lock() is currently smp_mb() > > for CONFIG_PPC and a no-op otherwise. It would be better to instead > > provide an architecture-selectable Kconfig option, and select the > > strength of smp_mb__after_unlock_lock() based on that option. This > > commit therefore creates CONFIG_ARCH_WEAK_RELACQ, has PPC select it, > > and bases the definition of smp_mb__after_unlock_lock() on this new > > CONFIG_ARCH_WEAK_RELACQ Kconfig option. > > > > Reported-by: Ingo Molnar > > Signed-off-by: Paul E. McKenney > > Cc: Peter Zijlstra > > Cc: Will Deacon > > Cc: Boqun Feng > > Cc: Benjamin Herrenschmidt > > Cc: Paul Mackerras > > Cc: Michael Ellerman > > Cc: > > Personally I'd call it ARCH_WEAK_RELEASE_ACQUIRE, which is longer but > clearer I think. But it's not a big deal, so which ever you prefer. ARCH_WEAK_RELEASE_ACQUIRE it is! > Acked-by: Michael Ellerman Applied, thank you! Thanx, Paul
Re: [PATCH tip/core/rcu 2/3] srcu: Force full grace-period ordering
"Paul E. McKenney"writes: > On Sat, Jan 14, 2017 at 11:54:17AM -0800, Paul E. McKenney wrote: >> On Sat, Jan 14, 2017 at 10:35:50AM +0100, Ingo Molnar wrote: >> > * Paul E. McKenney wrote: > > [ . . . ] > >> > > + */ >> > > +#ifdef CONFIG_PPC >> > > +#define smp_mb__after_unlock_lock() smp_mb() /* Full ordering for >> > > lock. */ >> > > +#else /* #ifdef CONFIG_PPC */ >> > > +#define smp_mb__after_unlock_lock() do { } while (0) >> > > +#endif /* #else #ifdef CONFIG_PPC */ >> > >> > Yeah, so I realize that this was pre-existing code, but putting >> > CONFIG_$ARCH >> > #ifdefs into generic headers is generally frowned upon. >> > >> > The canonical approach would be either to define a helper Kconfig variable >> > that >> > can be set by PPC (but other architectures don't need to set it), or to >> > expose a >> > suitable macro (function) for architectures to define in their barrier.h >> > arch >> > header file. >> >> Very well, I will add a separate commit for this. 4.11 OK? > > Does the patch below seem reasonable? > > Thanx, Paul > > > > commit 271c0601237c41a279f975563e13837bace0df03 > Author: Paul E. McKenney > Date: Sat Jan 14 13:32:50 2017 -0800 > > rcu: Make arch select smp_mb__after_unlock_lock() strength > > The definition of smp_mb__after_unlock_lock() is currently smp_mb() > for CONFIG_PPC and a no-op otherwise. It would be better to instead > provide an architecture-selectable Kconfig option, and select the > strength of smp_mb__after_unlock_lock() based on that option. This > commit therefore creates CONFIG_ARCH_WEAK_RELACQ, has PPC select it, > and bases the definition of smp_mb__after_unlock_lock() on this new > CONFIG_ARCH_WEAK_RELACQ Kconfig option. > > Reported-by: Ingo Molnar > Signed-off-by: Paul E. McKenney > Cc: Peter Zijlstra > Cc: Will Deacon > Cc: Boqun Feng > Cc: Benjamin Herrenschmidt > Cc: Paul Mackerras > Cc: Michael Ellerman > Cc: Personally I'd call it ARCH_WEAK_RELEASE_ACQUIRE, which is longer but clearer I think. But it's not a big deal, so which ever you prefer. Acked-by: Michael Ellerman cheers
Re: [PATCH tip/core/rcu 2/3] srcu: Force full grace-period ordering
* Paul E. McKenneywrote: > On Sun, Jan 15, 2017 at 10:40:58AM +0100, Ingo Molnar wrote: > > > > * Paul E. McKenney wrote: > > > > > > [sounds of rummaging around in the Git tree] > > > > > > > > I found this commit of yours from ancient history (more than a year > > > > ago!): > > > > > > > > commit 12d560f4ea87030667438a169912380be00cea4b > > > > Author: Paul E. McKenney > > > > Date: Tue Jul 14 18:35:23 2015 -0700 > > > > > > > > rcu,locking: Privatize smp_mb__after_unlock_lock() > > > > > > > > RCU is the only thing that uses smp_mb__after_unlock_lock(), and is > > > > likely the only thing that ever will use it, so this commit makes > > > > this > > > > macro private to RCU. > > > > > > > > Signed-off-by: Paul E. McKenney > > > > Cc: Will Deacon > > > > Cc: Peter Zijlstra > > > > Cc: Benjamin Herrenschmidt > > > > Cc: "linux-a...@vger.kernel.org" > > > > > > > > So I concur and I'm fine with your patch - or with the status quo code > > > > as well. > > > > > > I already have the patch queued, so how about I keep it if I get an ack > > > from the powerpc guys and drop it otherwise? > > > > Yeah, sounds good! Your patch made me look up 'RelAcq' so it has > > documentation > > value as well ;-) > > ;-) ;-) ;-) > > Looking forward, my guess would be that if some other code needs > smp_mb__after_unlock_lock() or if some other architecture needs > non-smb_mb() special handling, I should consider making it work the > same as smp_mb__after_atomic() and friends. Does that seem like a > reasonable thought? Yeah, absolutely - it's just that the pattern triggered the 'this looks a bit too specialized' response in me, but after seeing the details (again ...) I agree that this time is different! Thanks, Ingo
Re: [PATCH tip/core/rcu 2/3] srcu: Force full grace-period ordering
On Sun, Jan 15, 2017 at 10:40:58AM +0100, Ingo Molnar wrote: > > * Paul E. McKenneywrote: > > > > [sounds of rummaging around in the Git tree] > > > > > > I found this commit of yours from ancient history (more than a year ago!): > > > > > > commit 12d560f4ea87030667438a169912380be00cea4b > > > Author: Paul E. McKenney > > > Date: Tue Jul 14 18:35:23 2015 -0700 > > > > > > rcu,locking: Privatize smp_mb__after_unlock_lock() > > > > > > RCU is the only thing that uses smp_mb__after_unlock_lock(), and is > > > likely the only thing that ever will use it, so this commit makes this > > > macro private to RCU. > > > > > > Signed-off-by: Paul E. McKenney > > > Cc: Will Deacon > > > Cc: Peter Zijlstra > > > Cc: Benjamin Herrenschmidt > > > Cc: "linux-a...@vger.kernel.org" > > > > > > So I concur and I'm fine with your patch - or with the status quo code as > > > well. > > > > I already have the patch queued, so how about I keep it if I get an ack > > from the powerpc guys and drop it otherwise? > > Yeah, sounds good! Your patch made me look up 'RelAcq' so it has > documentation > value as well ;-) ;-) ;-) ;-) Looking forward, my guess would be that if some other code needs smp_mb__after_unlock_lock() or if some other architecture needs non-smb_mb() special handling, I should consider making it work the same as smp_mb__after_atomic() and friends. Does that seem like a reasonable thought? Thanx, Paul
Re: [PATCH tip/core/rcu 2/3] srcu: Force full grace-period ordering
* Paul E. McKenneywrote: > > [sounds of rummaging around in the Git tree] > > > > I found this commit of yours from ancient history (more than a year ago!): > > > > commit 12d560f4ea87030667438a169912380be00cea4b > > Author: Paul E. McKenney > > Date: Tue Jul 14 18:35:23 2015 -0700 > > > > rcu,locking: Privatize smp_mb__after_unlock_lock() > > > > RCU is the only thing that uses smp_mb__after_unlock_lock(), and is > > likely the only thing that ever will use it, so this commit makes this > > macro private to RCU. > > > > Signed-off-by: Paul E. McKenney > > Cc: Will Deacon > > Cc: Peter Zijlstra > > Cc: Benjamin Herrenschmidt > > Cc: "linux-a...@vger.kernel.org" > > > > So I concur and I'm fine with your patch - or with the status quo code as > > well. > > I already have the patch queued, so how about I keep it if I get an ack > from the powerpc guys and drop it otherwise? Yeah, sounds good! Your patch made me look up 'RelAcq' so it has documentation value as well ;-) Thanks, Ingo
Re: [PATCH tip/core/rcu 2/3] srcu: Force full grace-period ordering
On Sun, Jan 15, 2017 at 08:57:11AM +0100, Ingo Molnar wrote: > > * Paul E. McKenneywrote: > > > On Sun, Jan 15, 2017 at 08:11:23AM +0100, Ingo Molnar wrote: > > > > > > * Paul E. McKenney wrote: > > > > > > > diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h > > > > index 357b32aaea48..5fdfe874229e 100644 > > > > --- a/include/linux/rcupdate.h > > > > +++ b/include/linux/rcupdate.h > > > > @@ -1175,11 +1175,11 @@ do { \ > > > > * if the UNLOCK and LOCK are executed by the same CPU or if the > > > > * UNLOCK and LOCK operate on the same lock variable. > > > > */ > > > > -#ifdef CONFIG_PPC > > > > +#ifdef CONFIG_ARCH_WEAK_RELACQ > > > > #define smp_mb__after_unlock_lock()smp_mb() /* Full ordering for > > > > lock. */ > > > > -#else /* #ifdef CONFIG_PPC */ > > > > +#else /* #ifdef CONFIG_ARCH_WEAK_RELACQ */ > > > > #define smp_mb__after_unlock_lock()do { } while (0) > > > > -#endif /* #else #ifdef CONFIG_PPC */ > > > > +#endif /* #else #ifdef CONFIG_ARCH_WEAK_RELACQ */ > > > > > > > > > > > > > > So at the risk of sounding totally pedantic, why not structure it like > > > the > > > existing smp_mb__before/after*() primitives in barrier.h? > > > > > > That allows asm-generic/barrier.h to pick up the definition - for example > > > in the > > > case of smp_acquire__after_ctrl_dep() we do: > > > > > > #ifndef smp_acquire__after_ctrl_dep > > > #define smp_acquire__after_ctrl_dep() smp_rmb() > > > #endif > > > > > > Which allows Tile to relax it: > > > > > > arch/tile/include/asm/barrier.h:#define smp_acquire__after_ctrl_dep() > > > barrier() > > > > > > I.e. I'd move the API definition out of rcupdate.h and into barrier.h - > > > even > > > though tree-RCU is the only user of this barrier type. > > > > I wouldn't have any problem with that, however, some time back it was > > moved into RCU because (you guessed it!) RCU is the only user. ;-) > > Indeed ... > > [sounds of rummaging around in the Git tree] > > I found this commit of yours from ancient history (more than a year ago!): > > commit 12d560f4ea87030667438a169912380be00cea4b > Author: Paul E. McKenney > Date: Tue Jul 14 18:35:23 2015 -0700 > > rcu,locking: Privatize smp_mb__after_unlock_lock() > > RCU is the only thing that uses smp_mb__after_unlock_lock(), and is > likely the only thing that ever will use it, so this commit makes this > macro private to RCU. > > Signed-off-by: Paul E. McKenney > Cc: Will Deacon > Cc: Peter Zijlstra > Cc: Benjamin Herrenschmidt > Cc: "linux-a...@vger.kernel.org" > > So I concur and I'm fine with your patch - or with the status quo code as > well. I already have the patch queued, so how about I keep it if I get an ack from the powerpc guys and drop it otherwise? Thanx, Paul
Re: [PATCH tip/core/rcu 2/3] srcu: Force full grace-period ordering
* Paul E. McKenneywrote: > On Sun, Jan 15, 2017 at 08:11:23AM +0100, Ingo Molnar wrote: > > > > * Paul E. McKenney wrote: > > > > > diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h > > > index 357b32aaea48..5fdfe874229e 100644 > > > --- a/include/linux/rcupdate.h > > > +++ b/include/linux/rcupdate.h > > > @@ -1175,11 +1175,11 @@ do { \ > > > * if the UNLOCK and LOCK are executed by the same CPU or if the > > > * UNLOCK and LOCK operate on the same lock variable. > > > */ > > > -#ifdef CONFIG_PPC > > > +#ifdef CONFIG_ARCH_WEAK_RELACQ > > > #define smp_mb__after_unlock_lock() smp_mb() /* Full ordering for > > > lock. */ > > > -#else /* #ifdef CONFIG_PPC */ > > > +#else /* #ifdef CONFIG_ARCH_WEAK_RELACQ */ > > > #define smp_mb__after_unlock_lock() do { } while (0) > > > -#endif /* #else #ifdef CONFIG_PPC */ > > > +#endif /* #else #ifdef CONFIG_ARCH_WEAK_RELACQ */ > > > > > > > > > > So at the risk of sounding totally pedantic, why not structure it like the > > existing smp_mb__before/after*() primitives in barrier.h? > > > > That allows asm-generic/barrier.h to pick up the definition - for example > > in the > > case of smp_acquire__after_ctrl_dep() we do: > > > > #ifndef smp_acquire__after_ctrl_dep > > #define smp_acquire__after_ctrl_dep() smp_rmb() > > #endif > > > > Which allows Tile to relax it: > > > > arch/tile/include/asm/barrier.h:#define smp_acquire__after_ctrl_dep() > > barrier() > > > > I.e. I'd move the API definition out of rcupdate.h and into barrier.h - > > even > > though tree-RCU is the only user of this barrier type. > > I wouldn't have any problem with that, however, some time back it was > moved into RCU because (you guessed it!) RCU is the only user. ;-) Indeed ... [sounds of rummaging around in the Git tree] I found this commit of yours from ancient history (more than a year ago!): commit 12d560f4ea87030667438a169912380be00cea4b Author: Paul E. McKenney Date: Tue Jul 14 18:35:23 2015 -0700 rcu,locking: Privatize smp_mb__after_unlock_lock() RCU is the only thing that uses smp_mb__after_unlock_lock(), and is likely the only thing that ever will use it, so this commit makes this macro private to RCU. Signed-off-by: Paul E. McKenney Cc: Will Deacon Cc: Peter Zijlstra Cc: Benjamin Herrenschmidt Cc: "linux-a...@vger.kernel.org" So I concur and I'm fine with your patch - or with the status quo code as well. Thanks, Ingo
Re: [PATCH tip/core/rcu 2/3] srcu: Force full grace-period ordering
On Sun, Jan 15, 2017 at 08:11:23AM +0100, Ingo Molnar wrote: > > * Paul E. McKenneywrote: > > > diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h > > index 357b32aaea48..5fdfe874229e 100644 > > --- a/include/linux/rcupdate.h > > +++ b/include/linux/rcupdate.h > > @@ -1175,11 +1175,11 @@ do { \ > > * if the UNLOCK and LOCK are executed by the same CPU or if the > > * UNLOCK and LOCK operate on the same lock variable. > > */ > > -#ifdef CONFIG_PPC > > +#ifdef CONFIG_ARCH_WEAK_RELACQ > > #define smp_mb__after_unlock_lock()smp_mb() /* Full ordering for > > lock. */ > > -#else /* #ifdef CONFIG_PPC */ > > +#else /* #ifdef CONFIG_ARCH_WEAK_RELACQ */ > > #define smp_mb__after_unlock_lock()do { } while (0) > > -#endif /* #else #ifdef CONFIG_PPC */ > > +#endif /* #else #ifdef CONFIG_ARCH_WEAK_RELACQ */ > > > > > > So at the risk of sounding totally pedantic, why not structure it like the > existing smp_mb__before/after*() primitives in barrier.h? > > That allows asm-generic/barrier.h to pick up the definition - for example in > the > case of smp_acquire__after_ctrl_dep() we do: > > #ifndef smp_acquire__after_ctrl_dep > #define smp_acquire__after_ctrl_dep() smp_rmb() > #endif > > Which allows Tile to relax it: > > arch/tile/include/asm/barrier.h:#define smp_acquire__after_ctrl_dep() > barrier() > > I.e. I'd move the API definition out of rcupdate.h and into barrier.h - even > though tree-RCU is the only user of this barrier type. I wouldn't have any problem with that, however, some time back it was moved into RCU because (you guessed it!) RCU is the only user. ;-) Thanx, Paul
Re: [PATCH tip/core/rcu 2/3] srcu: Force full grace-period ordering
* Paul E. McKenneywrote: > diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h > index 357b32aaea48..5fdfe874229e 100644 > --- a/include/linux/rcupdate.h > +++ b/include/linux/rcupdate.h > @@ -1175,11 +1175,11 @@ do { \ > * if the UNLOCK and LOCK are executed by the same CPU or if the > * UNLOCK and LOCK operate on the same lock variable. > */ > -#ifdef CONFIG_PPC > +#ifdef CONFIG_ARCH_WEAK_RELACQ > #define smp_mb__after_unlock_lock() smp_mb() /* Full ordering for lock. */ > -#else /* #ifdef CONFIG_PPC */ > +#else /* #ifdef CONFIG_ARCH_WEAK_RELACQ */ > #define smp_mb__after_unlock_lock() do { } while (0) > -#endif /* #else #ifdef CONFIG_PPC */ > +#endif /* #else #ifdef CONFIG_ARCH_WEAK_RELACQ */ > > So at the risk of sounding totally pedantic, why not structure it like the existing smp_mb__before/after*() primitives in barrier.h? That allows asm-generic/barrier.h to pick up the definition - for example in the case of smp_acquire__after_ctrl_dep() we do: #ifndef smp_acquire__after_ctrl_dep #define smp_acquire__after_ctrl_dep() smp_rmb() #endif Which allows Tile to relax it: arch/tile/include/asm/barrier.h:#define smp_acquire__after_ctrl_dep() barrier() I.e. I'd move the API definition out of rcupdate.h and into barrier.h - even though tree-RCU is the only user of this barrier type. Thanks, Ingo
Re: [PATCH tip/core/rcu 2/3] srcu: Force full grace-period ordering
On Sat, Jan 14, 2017 at 11:54:17AM -0800, Paul E. McKenney wrote: > On Sat, Jan 14, 2017 at 10:35:50AM +0100, Ingo Molnar wrote: > > * Paul E. McKenneywrote: [ . . . ] > > > + */ > > > +#ifdef CONFIG_PPC > > > +#define smp_mb__after_unlock_lock() smp_mb() /* Full ordering for > > > lock. */ > > > +#else /* #ifdef CONFIG_PPC */ > > > +#define smp_mb__after_unlock_lock() do { } while (0) > > > +#endif /* #else #ifdef CONFIG_PPC */ > > > > Yeah, so I realize that this was pre-existing code, but putting CONFIG_$ARCH > > #ifdefs into generic headers is generally frowned upon. > > > > The canonical approach would be either to define a helper Kconfig variable > > that > > can be set by PPC (but other architectures don't need to set it), or to > > expose a > > suitable macro (function) for architectures to define in their barrier.h > > arch > > header file. > > Very well, I will add a separate commit for this. 4.11 OK? Does the patch below seem reasonable? Thanx, Paul commit 271c0601237c41a279f975563e13837bace0df03 Author: Paul E. McKenney Date: Sat Jan 14 13:32:50 2017 -0800 rcu: Make arch select smp_mb__after_unlock_lock() strength The definition of smp_mb__after_unlock_lock() is currently smp_mb() for CONFIG_PPC and a no-op otherwise. It would be better to instead provide an architecture-selectable Kconfig option, and select the strength of smp_mb__after_unlock_lock() based on that option. This commit therefore creates CONFIG_ARCH_WEAK_RELACQ, has PPC select it, and bases the definition of smp_mb__after_unlock_lock() on this new CONFIG_ARCH_WEAK_RELACQ Kconfig option. Reported-by: Ingo Molnar Signed-off-by: Paul E. McKenney Cc: Peter Zijlstra Cc: Will Deacon Cc: Boqun Feng Cc: Benjamin Herrenschmidt Cc: Paul Mackerras Cc: Michael Ellerman Cc: diff --git a/arch/Kconfig b/arch/Kconfig index 99839c23d453..94dd90d33f95 100644 --- a/arch/Kconfig +++ b/arch/Kconfig @@ -316,6 +316,9 @@ config HAVE_CMPXCHG_LOCAL config HAVE_CMPXCHG_DOUBLE bool +config ARCH_WEAK_RELACQ + bool + config ARCH_WANT_IPC_PARSE_VERSION bool diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig index a8ee573fe610..e7083d27271e 100644 --- a/arch/powerpc/Kconfig +++ b/arch/powerpc/Kconfig @@ -165,6 +165,7 @@ config PPC select HAVE_ARCH_HARDENED_USERCOPY select HAVE_KERNEL_GZIP select HAVE_CC_STACKPROTECTOR + select ARCH_WEAK_RELACQ config GENERIC_CSUM def_bool CPU_LITTLE_ENDIAN diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index 357b32aaea48..5fdfe874229e 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -1175,11 +1175,11 @@ do { \ * if the UNLOCK and LOCK are executed by the same CPU or if the * UNLOCK and LOCK operate on the same lock variable. */ -#ifdef CONFIG_PPC +#ifdef CONFIG_ARCH_WEAK_RELACQ #define smp_mb__after_unlock_lock()smp_mb() /* Full ordering for lock. */ -#else /* #ifdef CONFIG_PPC */ +#else /* #ifdef CONFIG_ARCH_WEAK_RELACQ */ #define smp_mb__after_unlock_lock()do { } while (0) -#endif /* #else #ifdef CONFIG_PPC */ +#endif /* #else #ifdef CONFIG_ARCH_WEAK_RELACQ */ #endif /* __LINUX_RCUPDATE_H */