| Message ID | 1507573730-8083-1-git-send-email-mark.rutland@arm.com |
|---|---|
| Headers | show |
| Series | Preparatory work to kill off ACCESS_ONCE() | expand |
On Mon, Oct 09, 2017 at 07:28:37PM +0100, Mark Rutland wrote: > Hi all, > > There's a general want to kill off ACCESS_ONCE(), which is required to kill off > smp_read_barrier_depends(), and to support debug features which require > instrumenting reads and writes separately. > > Thanks to preparatory work by a number of people, it's largely possible to > script this with the Coccinelle patch below. However, this breaks a handful of > cases, and renders some comments stale. > > This series fixes up said cases, and comments. Where fixups have been made, > I've converted the entire file for consistency. The remaining code can be > converted by Coccinelle script, allowing for the subsequent removal of > ACCESS_ONCE(). > > I've pushed this series, complete with an example treewide conversion of > v4.14-rc4 to my core/access-once branch [1,2]. And this all that is left, aside from definitions and comments associated with those definitions. Cool! Feel free to pull this into your preparation series. Thanx, Paul ------------------------------------------------------------------------ commit ed940234966f4857e23dd5f16aa8f200fc85dac6 Author: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Date: Mon Oct 9 12:59:18 2017 -0700 treewide: Kill off remaining ACCESS_ONCE() This commit removes instances of ACCESS_ONCE() not located by Mark Rutland's coccinelle script, for example, those in complex macro definitions and those in comments. Removing ACCESS_ONCE() in favor of READ_ONCE() and WRITE_ONCE() provides tools such as KTSAN the read/write distinction that they need to better detect concurrency bugs. In addition, removing ACCESS_ONCE() is one necessary step towards removing special cases for DEC Alpha from the Linux-kernel memory model. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> diff --git a/Documentation/filesystems/path-lookup.md b/Documentation/filesystems/path-lookup.md index 1b39e084a2b2..50ea32a51626 100644 --- a/Documentation/filesystems/path-lookup.md +++ b/Documentation/filesystems/path-lookup.md @@ -826,9 +826,9 @@ If the filesystem may need to revalidate dcache entries, then *is* passed the dentry but does not have access to the `inode` or the `seq` number from the `nameidata`, so it needs to be extra careful when accessing fields in the dentry. This "extra care" typically -involves using `ACCESS_ONCE()` or the newer [`READ_ONCE()`] to access -fields, and verifying the result is not NULL before using it. This -pattern can be see in `nfs_lookup_revalidate()`. +involves using [`READ_ONCE()`] to access fields, and verifying the +result is not NULL before using it. This pattern can be see in +`nfs_lookup_revalidate()`. A pair of patterns ------------------ diff --git a/mm/memory.c b/mm/memory.c index a728bed16c20..cae514e7dcfc 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -3891,9 +3891,9 @@ static int handle_pte_fault(struct vm_fault *vmf) /* * some architectures can have larger ptes than wordsize, * e.g.ppc44x-defconfig has CONFIG_PTE_64BIT=y and - * CONFIG_32BIT=y, so READ_ONCE or ACCESS_ONCE cannot guarantee - * atomic accesses. The code below just needs a consistent - * view for the ifs and we later double check anyway with the + * CONFIG_32BIT=y, so READ_ONCE cannot guarantee atomic + * accesses. The code below just needs a consistent view + * for the ifs and we later double check anyway with the * ptl lock held. So here a barrier will do. */ barrier();