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Re: [PATCH v2] xen/arm64/atomic: Clear exclusive monitor on cmpxchg failure
- To: Jan Beulich <jbeulich@xxxxxxxx>
- From: ryoj <okamoto@xxxxxxxxxxxxx>
- Date: Fri, 11 Sep 2026 17:42:28 +0900
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- Cc: Hirokazu Takahashi <taka@xxxxxxxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Bertrand Marquis <bertrand.marquis@xxxxxxx>, Michal Orzel <michal.orzel@xxxxxxx>, Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Fri, 11 Sep 2026 08:42:51 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 9/9/26 15:31, Jan Beulich wrote:
On 09.09.2026 08:12, Ryoji Okamoto wrote:
When the value comparison fails in atomic_cmpxchg, the code branches
out without executing stxr, leaving the exclusive monitor in the
exclusive state set by ldxr.
Add `clrex` to the failure path to explicitly clear the exclusive
monitor.
Fixes: d2654a556835 ("xen: arm64: atomics")
Signed-off-by: Ryoji Okamoto <okamoto@xxxxxxxxxxxxx>
---
v2: Use tabs for indentation instead of spaces
Well, ...
--- a/xen/arch/arm/include/asm/arm64/atomic.h
+++ b/xen/arch/arm/include/asm/arm64/atomic.h
@@ -118,7 +118,9 @@ static inline int atomic_cmpxchg(atomic_t *v, int old, int
new)
" b.ne 2f\n"
" stxr %w0, %w4, %2\n"
" cbnz %w0, 1b\n"
-"2:"
+" b 3f\n"
... you now do here, but ...
+"2: clrex\n"
... still not here.
Jan
Hi Jan,
Thanks for the feedback on the indentation.
I'm withdrawing this patch, but I'll definitely keep this in mind for
the next time.
Regards,
--
Ryoji
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