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Peter Anvin" , Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@meta.com Subject: Re: [PATCH v2] cleanup: Remove NULL check from unconditional guards Message-ID: <20260512165514.GC2677887@noisy.programming.kicks-ass.net> References: <20260512071510.92451-1-d@ilvokhin.com> <20260512124557.GD1889694@noisy.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: EB5CC10000F X-Stat-Signature: 5xwhp44sj5e444geh4bkf4jm1o5yf555 X-Rspam-User: X-HE-Tag: 1778604921-582721 X-HE-Meta: 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 g9L1SRlg X0+bniz5JqtfLxgGlldodfaPdREyFjvSAjtcr1VN9KllmDKOETGzHajfTvxswCsVhZ0VHGJ+1pEbqrMRDtwVKCHCkLkLjIiqhmGP3xy1dhlKrDuQWBMqs7aPg90+TNqGrz6aa8QQRGcbvS4lVp3R2+JsUgwnoL3r2YlFGcHybu5rpkuYOdEUVz3SiigWsG96KgVHYIXaW0yGQgEqFgdLIDoWzjw== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, May 12, 2026 at 02:37:25PM +0000, Dmitry Ilvokhin wrote: > On Tue, May 12, 2026 at 02:45:57PM +0200, Peter Zijlstra wrote: > > > > What about class_irqdesc_lock_constructor() ? AFAICT > > __irq_get_desc_lock() can return NULL. > > Thanks for taking a look, Peter. Yes, that is actually a very good > catch. > > For some reason I naively thought __DEFINE_UNLOCK_GUARD() wouldn't be > used outside of include/linux/cleanup.h, but this is obviously wrong > assumption. There are cases, where DEFINE_LOCK_GUARD_1() doesn't fit > callers needs, so __DEFINE_UNLOCK_GUARD() is used directly. > > - kernel/irq/internals.h: the case you pointed out. Can be fixed by > moving the NULL check into the irqdesc_lock unlock expression > directly. > > - include/linux/tty_port.h: similar use case. NULL check can be moved > into tty_port_tty as well, similar to previous case. > > - kernel/sched/sched.h: lock and lock2 shouldn't be NULL at destructor > time, since they are dereferenced unconditionally at constructor. > > Below is example how this will look like. Does this look reasonable to > you, or would you prefer a different approach? Yeah, I don't mind changing things here, but like I said before, only after a full audit of every single user ;-) And yeah, fixing up those things shouldn't be hard, but it needs be done.