[PATCH 0/3] rculist: Fix list_entry_rcu to read ptr with, rcu_dereference_raw
Hi Paul and Josh, While running some benchmarks with rcu, I noticed that rculist had a performance issue compared to the non-rcu list. Having a closer look at the rlulist, I found that there is a bad usage of rcu_dereference_raw in list_entry_rcu(). Indeed, "typeof (*ptr) *__ptr = ptr;" reads ptr and "rcu_dereference_raw(__ptr)" forces read on the stack variable __ptr. However, ptr should be read with rcu_dereference_raw not the __ptr. This was introduced some years ago with commit 67bdbffd (2010-02-25). I am proposing to revert this part of the patch but probably this can be fixed differently. Fixing this showed 2 problems in the usage of list_entry_rcu. Since it touches other parts of kernel, I guess it requires ack from other maintainers. Thanks. PS: I will Cc the others maintainers when somebody confirms the problem. Signed-off-by: Patrick Marlier Cc: "Paul E. McKenney" Cc: Josh Triplett Cc: Arnd Bergmann -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
[PATCH 0/3] rculist: Fix list_entry_rcu to read ptr with, rcu_dereference_raw
Hi Paul and Josh, While running some benchmarks with rcu, I noticed that rculist had a performance issue compared to the non-rcu list. Having a closer look at the rlulist, I found that there is a bad usage of rcu_dereference_raw in list_entry_rcu(). Indeed, typeof (*ptr) *__ptr = ptr; reads ptr and rcu_dereference_raw(__ptr) forces read on the stack variable __ptr. However, ptr should be read with rcu_dereference_raw not the __ptr. This was introduced some years ago with commit 67bdbffd (2010-02-25). I am proposing to revert this part of the patch but probably this can be fixed differently. Fixing this showed 2 problems in the usage of list_entry_rcu. Since it touches other parts of kernel, I guess it requires ack from other maintainers. Thanks. PS: I will Cc the others maintainers when somebody confirms the problem. Signed-off-by: Patrick Marlier patrick.marl...@gmail.com Cc: Paul E. McKenney paul...@linux.vnet.ibm.com Cc: Josh Triplett j...@joshtriplett.org Cc: Arnd Bergmann a...@arndb.de -- To unsubscribe from this list: send the line unsubscribe linux-kernel in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
