Messages in this thread Patch in this message | | | Date | Wed, 21 Feb 2018 12:15:56 -0500 (EST) | From | Alan Stern <> | Subject | [PATCH] tools/memory-model: update: remove rb-dep, smp_read_barrier_depends, and lockless_dereference |
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Commit bf28ae562744 ("tools/memory-model: Remove rb-dep, smp_read_barrier_depends, and lockless_dereference") was accidentally merged too early, while it was still in RFC form. This patch adds in the missing pieces.
Akira pointed out some typos in the original patch, and he noted that cheatsheet.txt should be updated to indicate how unsuccessful RMW operations relate to address dependencies.
Andrea pointed out that the macro for rcu_dereference() in linux.def should now use the "once" annotation instead of "deref". He also suggested that the comments should mention commit 5a8897cc7631 ("locking/atomics/alpha: Add smp_read_barrier_depends() to _release()/_relaxed() atomics") as an important precursor, and he contributed commit cb13b424e986 ("locking/xchg/alpha: Add unconditional memory barrier to cmpxchg()"), another prerequisite.
Signed-off-by: Alan Stern <stern@rowland.harvard.edu> Suggested-by: Akira Yokosawa <akiyks@gmail.com> Suggested-by: Andrea Parri <parri.andrea@gmail.com> Fixes: bf28ae562744 ("tools/memory-model: Remove rb-dep, smp_read_barrier_depends, and lockless_dereference")
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tools/memory-model/Documentation/cheatsheet.txt | 6 +++--- tools/memory-model/Documentation/explanation.txt | 4 ++-- tools/memory-model/linux-kernel.def | 2 +- 3 files changed, 6 insertions(+), 6 deletions(-)
Index: usb-4.x/tools/memory-model/Documentation/cheatsheet.txt =================================================================== --- usb-4.x.orig/tools/memory-model/Documentation/cheatsheet.txt +++ usb-4.x/tools/memory-model/Documentation/cheatsheet.txt @@ -1,11 +1,11 @@ Prior Operation Subsequent Operation --------------- --------------------------- C Self R W RWM Self R W DR DW RMW SV - __ ---- - - --- ---- - - -- -- --- -- + -- ---- - - --- ---- - - -- -- --- -- Store, e.g., WRITE_ONCE() Y Y -Load, e.g., READ_ONCE() Y Y Y -Unsuccessful RMW operation Y Y Y +Load, e.g., READ_ONCE() Y Y Y Y +Unsuccessful RMW operation Y Y Y Y rcu_dereference() Y Y Y Y Successful *_acquire() R Y Y Y Y Y Y Successful *_release() C Y Y Y W Y Index: usb-4.x/tools/memory-model/Documentation/explanation.txt =================================================================== --- usb-4.x.orig/tools/memory-model/Documentation/explanation.txt +++ usb-4.x/tools/memory-model/Documentation/explanation.txt @@ -826,7 +826,7 @@ A-cumulative; they only affect the propa executed on C before the fence (i.e., those which precede the fence in program order). -read_lock(), rcu_read_unlock(), and synchronize_rcu() fences have +read_read_lock(), rcu_read_unlock(), and synchronize_rcu() fences have other properties which we discuss later. @@ -1138,7 +1138,7 @@ final effect is that even though the two program order, it appears that they aren't. This could not have happened if the local cache had processed the -incoming stores in FIFO order. In constrast, other architectures +incoming stores in FIFO order. By contrast, other architectures maintain at least the appearance of FIFO order. In practice, this difficulty is solved by inserting a special fence Index: usb-4.x/tools/memory-model/linux-kernel.def =================================================================== --- usb-4.x.orig/tools/memory-model/linux-kernel.def +++ usb-4.x/tools/memory-model/linux-kernel.def @@ -13,7 +13,7 @@ WRITE_ONCE(X,V) { __store{once}(X,V); } smp_store_release(X,V) { __store{release}(*X,V); } smp_load_acquire(X) __load{acquire}(*X) rcu_assign_pointer(X,V) { __store{release}(X,V); } -rcu_dereference(X) __load{deref}(X) +rcu_dereference(X) __load{once}(X) // Fences smp_mb() { __fence{mb} ; }
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