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Merge tag 'kcsan.2023.04.04a' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu

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Pull KCSAN updates from Paul McKenney:
 "Kernel concurrency sanitizer (KCSAN) updates for v6.4

  This fixes kernel-doc warnings and also updates instrumentation from
  READ_ONCE() to volatile in order to avoid unaligned load-acquire
  instructions on arm64 in kernels built with LTO"

* tag 'kcsan.2023.04.04a' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu:
  kcsan: Avoid READ_ONCE() in read_instrumented_memory()
  instrumented.h: Fix all kernel-doc format warnings
This commit is contained in:
Linus Torvalds
2023-04-24 11:46:53 -07:00
parent 1a0beef98b 8dec88070d
commit 022e32094e
2 changed files with 39 additions and 41 deletions
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17
kernel/kcsan/core.c
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@@ -337,11 +337,20 @@ static void delay_access(int type)
*/
static __always_inline u64 read_instrumented_memory(const volatile void *ptr, size_t size)
{
/*
* In the below we don't necessarily need the read of the location to
* be atomic, and we don't use READ_ONCE(), since all we need for race
* detection is to observe 2 different values.
*
* Furthermore, on certain architectures (such as arm64), READ_ONCE()
* may turn into more complex instructions than a plain load that cannot
* do unaligned accesses.
*/
switch (size) {
case 1: return READ_ONCE(*(const u8 *)ptr);
case 2: return READ_ONCE(*(const u16 *)ptr);
case 4: return READ_ONCE(*(const u32 *)ptr);
case 8: return READ_ONCE(*(const u64 *)ptr);
case 1: return *(const volatile u8 *)ptr;
case 2: return *(const volatile u16 *)ptr;
case 4: return *(const volatile u32 *)ptr;
case 8: return *(const volatile u64 *)ptr;
default: return 0; /* Ignore; we do not diff the values. */
}
}