On Thu, 10 Jan 2019, Paul E. McKenney wrote: > On Thu, Jan 10, 2019 at 09:40:24AM +0100, Andrea Parri wrote: > > > > > > It seems that > > > > > > > > > > > > 1b52d0186177 ("tools/memory-model: Model smp_mb__after_unlock_lock()") > > > > > > > > > > > > from linux-rcu/dev got lost; this also needs an ack (probably yours! ;D, > > > > > > considered that, IIRC, you introduced the primitive and RCU is currently > > > > > > its only user.) > > > > > > > > > > That commit is in -tip: > > > > > > > > > > 4607abbcf464 ("tools/memory-model: Model smp_mb__after_unlock_lock()") > > > > > > > > > > So it has already left my -rcu tree. ;-) > > > > > > > > Oh, you're right: now I see the commit (e.g., with "git show"), but I > > > > don't see the corresponding changes applied to the tree. > > > > > > > > https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git/commit/?h=locking/core&id=4607abbcf464ea2be14da444215d05c73025cf6e > > > > https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git/tree/tools/memory-model/linux-kernel.bell?h=locking/core > > > > > > > > Is this expected? > > > > > > Are you asking why it is in -tip but not in mainline? I am not sure, > > > but given that the merge window was over the holiday season and that > > > the length of the merge window proved to be shorter than many people > > > expected it to be, I am not too surprised. ;-) > > > > Mmh, let me try again: > > > > $ git clone git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git > > $ cd tip > > $ git checkout -b locking/core origin/locking/core > > > > $ git show 4607abbcf464 > > commit 4607abbcf464ea2be14da444215d05c73025cf6e > > Author: Andrea Parri <andrea.parri@xxxxxxxxxxxxxxxxxxxx> > > Date: Mon Dec 3 15:04:49 2018 -0800 > > > > tools/memory-model: Model smp_mb__after_unlock_lock() > > > > $ cd tools/memory-model > > $ herd7 -conf linux-kernel.cfg after-unlock-lock-same-cpu.litmus > > File "after-unlock-lock-same-cpu.litmus": Unknown macro smp_mb__after_unlock_lock (User error) > > > > [aka, linux-kernel.def in tip:locking/core does not have the > > smp_mb__after_unlock_lock() added by 4607abbcf464] > > Color me confused: > > ------------------------------------------------------------------------ > > $ git checkout 4607abbcf464Checking out files: 100% (18397/18397), done. > Previous HEAD position was 4e284b1bf15a rcu: Remove wrapper definitions for obsolete RCU update functions > HEAD is now at 4607abbcf464 tools/memory-model: Model smp_mb__after_unlock_lock() > $ grep smp_mb__after_unlock_lock tools/memory-model/linux-kernel.def > smp_mb__after_unlock_lock() { __fence{after-unlock-lock}; } > > ------------------------------------------------------------------------ > > In addition, it handles this litmus test just fine: > > ------------------------------------------------------------------------ > > C MP+polocks > > (* > * Result: Never > * > * This litmus test demonstrates how lock acquisitions and releases can > * stand in for smp_load_acquire() and smp_store_release(), respectively. > * In other words, when holding a given lock (or indeed after releasing a > * given lock), a CPU is not only guaranteed to see the accesses that other > * CPUs made while previously holding that lock, it is also guaranteed > * to see all prior accesses by those other CPUs. > *) > > {} > > P0(int *x, int *y, spinlock_t *mylock) > { > WRITE_ONCE(*x, 1); > spin_lock(mylock); > smp_mb__after_unlock_lock(); > WRITE_ONCE(*y, 1); > spin_unlock(mylock); > } > > P1(int *x, int *y, spinlock_t *mylock) > { > int r0; > int r1; > > spin_lock(mylock); > r0 = READ_ONCE(*y); > spin_unlock(mylock); > r1 = READ_ONCE(*x); > } > > exists (1:r0=1 /\ 1:r1=0) > > ------------------------------------------------------------------------ > > Again, color me confused. Andrea's point is that while the 1b52d0186177 commit is present in the tip repository, it isn't in the locking/core branch. Alan