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Thu, 06 Nov 2025 01:36:25 -0800 (PST) Message-ID: Date: Thu, 6 Nov 2025 10:36:28 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] misra: address Rule 11.3 in spin_unlock_common() To: Andrew Cooper , Dmytro Prokopchuk1 Cc: Alistair Francis , Bob Eshleman , Connor Davis , Oleksii Kurochko , Anthony PERARD , Michal Orzel , Julien Grall , =?UTF-8?Q?Roger_Pau_Monn=C3=A9?= , Stefano Stabellini , "xen-devel@lists.xenproject.org" References: <812bf5574cb44727c561e0ebc3a54848823ed490.1762163173.git.dmytro_prokopchuk1@epam.com> <7fb6ca46-3806-4aa5-a642-28384d6b944c@citrix.com> Content-Language: en-US From: Jan Beulich Autocrypt: addr=jbeulich@suse.com; keydata= xsDiBFk3nEQRBADAEaSw6zC/EJkiwGPXbWtPxl2xCdSoeepS07jW8UgcHNurfHvUzogEq5xk hu507c3BarVjyWCJOylMNR98Yd8VqD9UfmX0Hb8/BrA+Hl6/DB/eqGptrf4BSRwcZQM32aZK 7Pj2XbGWIUrZrd70x1eAP9QE3P79Y2oLrsCgbZJfEwCgvz9JjGmQqQkRiTVzlZVCJYcyGGsD /0tbFCzD2h20ahe8rC1gbb3K3qk+LpBtvjBu1RY9drYk0NymiGbJWZgab6t1jM7sk2vuf0Py O9Hf9XBmK0uE9IgMaiCpc32XV9oASz6UJebwkX+zF2jG5I1BfnO9g7KlotcA/v5ClMjgo6Gl MDY4HxoSRu3i1cqqSDtVlt+AOVBJBACrZcnHAUSuCXBPy0jOlBhxPqRWv6ND4c9PH1xjQ3NP nxJuMBS8rnNg22uyfAgmBKNLpLgAGVRMZGaGoJObGf72s6TeIqKJo/LtggAS9qAUiuKVnygo 3wjfkS9A3DRO+SpU7JqWdsveeIQyeyEJ/8PTowmSQLakF+3fote9ybzd880fSmFuIEJldWxp Y2ggPGpiZXVsaWNoQHN1c2UuY29tPsJgBBMRAgAgBQJZN5xEAhsDBgsJCAcDAgQVAggDBBYC AwECHgECF4AACgkQoDSui/t3IH4J+wCfQ5jHdEjCRHj23O/5ttg9r9OIruwAn3103WUITZee e7Sbg12UgcQ5lv7SzsFNBFk3nEQQCACCuTjCjFOUdi5Nm244F+78kLghRcin/awv+IrTcIWF hUpSs1Y91iQQ7KItirz5uwCPlwejSJDQJLIS+QtJHaXDXeV6NI0Uef1hP20+y8qydDiVkv6l IreXjTb7DvksRgJNvCkWtYnlS3mYvQ9NzS9PhyALWbXnH6sIJd2O9lKS1Mrfq+y0IXCP10eS FFGg+Av3IQeFatkJAyju0PPthyTqxSI4lZYuJVPknzgaeuJv/2NccrPvmeDg6Coe7ZIeQ8Yj t0ARxu2xytAkkLCel1Lz1WLmwLstV30g80nkgZf/wr+/BXJW/oIvRlonUkxv+IbBM3dX2OV8 AmRv1ySWPTP7AAMFB/9PQK/VtlNUJvg8GXj9ootzrteGfVZVVT4XBJkfwBcpC/XcPzldjv+3 HYudvpdNK3lLujXeA5fLOH+Z/G9WBc5pFVSMocI71I8bT8lIAzreg0WvkWg5V2WZsUMlnDL9 mpwIGFhlbM3gfDMs7MPMu8YQRFVdUvtSpaAs8OFfGQ0ia3LGZcjA6Ik2+xcqscEJzNH+qh8V m5jjp28yZgaqTaRbg3M/+MTbMpicpZuqF4rnB0AQD12/3BNWDR6bmh+EkYSMcEIpQmBM51qM EKYTQGybRCjpnKHGOxG0rfFY1085mBDZCH5Kx0cl0HVJuQKC+dV2ZY5AqjcKwAxpE75MLFkr wkkEGBECAAkFAlk3nEQCGwwACgkQoDSui/t3IH7nnwCfcJWUDUFKdCsBH/E5d+0ZnMQi+G0A nAuWpQkjM1ASeQwSHEeAWPgskBQL In-Reply-To: <7fb6ca46-3806-4aa5-a642-28384d6b944c@citrix.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 03.11.2025 12:26, Andrew Cooper wrote: > On 03/11/2025 10:11 am, Dmytro Prokopchuk1 wrote: >> diff --git a/xen/common/spinlock.c b/xen/common/spinlock.c >> index 0389293b09..d9dc9998e6 100644 >> --- a/xen/common/spinlock.c >> +++ b/xen/common/spinlock.c >> @@ -367,7 +367,8 @@ static void always_inline spin_unlock_common(spinlock_tickets_t *t, >> LOCK_PROFILE_REL; >> rel_lock(debug); >> arch_lock_release_barrier(); >> - add_sized(&t->head, 1); >> + BUILD_BUG_ON(sizeof(t->head) != sizeof(uint16_t)); >> + add_u16_sized(&t->head, 1); > > This is an example where MISRA's opinions actively making the logic less > safe. > > It's not possible for add_sized() to use the wrong type (as it > calculates it internally), whereas it's quite possible to update the > BUILD_BUG_ON() and fail to adjust the add. > > Specifically, you've made it more complicated to reason about, and > created an opportunity to make an unsafe change where that opportunity > does not exist in the code as-is. > > Furthermore, read and write atomic have exactly the same internal > pattern as add_sized(), so how does this not just kick the can down the > road? +1 (fwiw) Jan