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locking/atomics, doc/filesystems: Convert ACCESS_ONCE() references
For several reasons, it is desirable to use {READ,WRITE}_ONCE() in preference to ACCESS_ONCE(), and new code is expected to use one of the former. So far, there's been no reason to change most existing uses of ACCESS_ONCE(), as these aren't currently harmful. However, for some features it is necessary to instrument reads and writes separately, which is not possible with ACCESS_ONCE(). This distinction is critical to correct operation. It's possible to transform the bulk of kernel code using the Coccinelle script below. However, this doesn't handle documentation, leaving references to ACCESS_ONCE() instances which have been removed. As a preparatory step, this patch converts the filesystems documentation to use {READ,WRITE}_ONCE() consistently. ---- virtual patch @ depends on patch @ expression E1, E2; @@ - ACCESS_ONCE(E1) = E2 + WRITE_ONCE(E1, E2) @ depends on patch @ expression E; @@ - ACCESS_ONCE(E) + READ_ONCE(E) ---- Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Acked-by: Will Deacon <will.deacon@arm.com> Acked-by: Mark Rutland <mark.rutland@arm.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: davem@davemloft.net Cc: linux-arch@vger.kernel.org Cc: mpe@ellerman.id.au Cc: shuah@kernel.org Cc: snitzer@redhat.com Cc: thor.thayer@linux.intel.com Cc: tj@kernel.org Cc: viro@zeniv.linux.org.uk Link: http://lkml.kernel.org/r/1508792849-3115-14-git-send-email-paulmck@linux.vnet.ibm.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
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@ -826,9 +826,9 @@ If the filesystem may need to revalidate dcache entries, then
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*is* passed the dentry but does not have access to the `inode` or the
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`seq` number from the `nameidata`, so it needs to be extra careful
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when accessing fields in the dentry. This "extra care" typically
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involves using `ACCESS_ONCE()` or the newer [`READ_ONCE()`] to access
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fields, and verifying the result is not NULL before using it. This
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pattern can be see in `nfs_lookup_revalidate()`.
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involves using [`READ_ONCE()`] to access fields, and verifying the
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result is not NULL before using it. This pattern can be seen in
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`nfs_lookup_revalidate()`.
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A pair of patterns
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------------------
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