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Biederman" , Adrian Reber , Thomas Gleixner , Jens Axboe , Alexei Starovoitov , "linux-fsdevel@vger.kernel.org" , "linux-kernel@vger.kernel.org" , linux-kselftest@vger.kernel.org, linux-mm@kvack.org, linux-security-module@vger.kernel.org, tiozhang , Luis Chamberlain , "Paulo Alcantara (SUSE)" , Sergey Senozhatsky , Frederic Weisbecker , YueHaibing , Paul Moore , Aleksa Sarai , Stefan Roesch , Chao Yu , xu xin , Jeff Layton , Jan Kara , David Hildenbrand , Dave Chinner , Shuah Khan , Elena Reshetova , David Windsor , Mateusz Guzik , Ard Biesheuvel , "Joel Fernandes (Google)" , "Matthew Wilcox (Oracle)" , Hans Liljestrand , Penglei Jiang , Lorenzo Stoakes , Adrian Ratiu , Ingo Molnar , "Peter Zijlstra (Intel)" , Cyrill Gorcunov , Eric Dumazet Subject: Re: [PATCH v17] exec: Fix dead-lock in de_thread with ptrace_attach Message-ID: References: <20251105143210.GA25535@redhat.com> <20251111-ankreiden-augen-eadcf9bbdfaa@brauner> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Scanned-By: MIMEDefang 3.0 on 10.30.177.17 X-Rspamd-Queue-Id: 3F6461C0010 X-Rspam-User: X-Rspamd-Server: rspam05 X-Stat-Signature: cy77dw1op3gkqd89q4zqrnragf7s8q4b X-HE-Tag: 1764602030-382018 X-HE-Meta: U2FsdGVkX1/nQjYos0RFtFp+plTWYLuhTEdv23g+yZ0VbZeUCaHgnyroVuQahMjQLoqChMil21NllyDHQKTCoUdHEnLvHFMUEP5r834oaYymOzvBlih+FK/PMUU/YdGi0FN6+NlZmBTL/jYYxdwBEs7LcGEzyY5PGGaOyLq+N3wqUKaeCbundPBTiCdFWJ2V01gXaeKSUluVF2WXKSiHy+lvgu763MM0m8ov+MdPF9rw7xYNYP+HIKxcLtJoijuSiqujrWVQyAeuiSRiJH4YkkuDJJDfxJ2ETHUjGmrC5IG5JuCGnFsZsAPwWKnyrR5pDGon+RpXc26Khq29qMi5K4q0j0u/+Ib6S2r2V9TSyJqf0XohayAWv0F3fPuzyIOnGF0YtMfRCD2C3rehjSlUylnGCZMC6xxf9ES0HLo3c2ox7ltMabQeOeOG2XZYZ232pb2RI7MQ/VATfOgyWqI+DrGNgP7aMAjvjOM4esLXipTUzQDkNgeULvLlQzCM+k+mvMndOZniMzjIkMvjGqna7c74lHyLHV576yKzDkOPyYNTXHVqUzdNiz963BSfMy905Lvg7QtcsdiymqIbcwl9aJlYZd5RwR2nneTc0jfJ2t1QNlqEl4T06omzpnxQxO6Dp/G84eAon1p4n9WdUMW7yvTrL6b8s1LyuMQ1T/F4TaLCavheVjHxeLHCUK/rJ+zDWpOtQ16VCoZnaAAyugi3Qb7mC+OMA93ynJdNR0NWuaD58Hv8bMIjfKbsiwQEc8C+aLIZuRLQcS67j9UWUMhiQYoOVr/Pc9jPaEYzzlSAocjc3XB1nM3ATFOxbW1Bn2x9EwL3XjbHK87SeMzDJUNFjwODjdKJfA6wHTtRjj158HuHKMrQhv7zB8mvQILpf515WkdOLEsz3Mu+1gA4dGVEgz3AXRG2ssz0KZWjf1X/M0EZ31NRmEw5Nxv537uwCOdgijsWTgPWNtThwaWCTL1 qMw0kDWK e9fEJon4O8WiMMwqD77SBwou3Rj/SF6LQ1p2WQlBCnytttyAzUPVkhpYHV3piVI2+9ku9BkXGhGW8AISZbQ+CoJR7EZ1wasix2SmUU6AlYvse58DrIS3Ek12lHXBKW3G78xYv+rsyehPPNOKsvP+QjM8pyciHHMijMj7STpP18oOH+w9Vyi01IaEBT/OsCR9IxM6z1d5g7XB4hIsyYcWO9xI5xQ== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 11/29, Bernd Edlinger wrote: > > On 11/23/25 19:32, Oleg Nesterov wrote: > > I don't follow. Do you mean PREEMPT_RT ? > > > > If yes. In this case spin_lock_irq() is rt_spin_lock() which doesn't disable irqs, > > it does rt_lock_lock() (takes rt_mutex) + migrate_disable(). > > > > I do think that spin/mutex/whatever_unlock() is always safe. In any order, and > > regardless of RT. > > > > It is hard to follow how linux implements that spin_lock_irq exactly, Yes ;) > but > to me it looks like it is done this way: > > include/linux/spinlock_api_smp.h:static inline void __raw_spin_lock_irq(raw_spinlock_t *lock) > include/linux/spinlock_api_smp.h-{ > include/linux/spinlock_api_smp.h- local_irq_disable(); > include/linux/spinlock_api_smp.h- preempt_disable(); > include/linux/spinlock_api_smp.h- spin_acquire(&lock->dep_map, 0, 0, _RET_IP_); > include/linux/spinlock_api_smp.h- LOCK_CONTENDED(lock, do_raw_spin_trylock, do_raw_spin_lock); > include/linux/spinlock_api_smp.h-} Again, I will assume you mean RT. In this case spinlock_t and raw_spinlock_t are not the same thing. include/linux/spinlock_types.h: typedef struct spinlock { struct rt_mutex_base lock; #ifdef CONFIG_DEBUG_LOCK_ALLOC struct lockdep_map dep_map; #endif } spinlock_t; include/linux/spinlock_rt.h: static __always_inline void spin_lock_irq(spinlock_t *lock) { rt_spin_lock(lock); } rt_spin_lock() doesn't disable irqs, it takes "rt_mutex_base lock" and disables migration. > so an explicit task switch while locka_irq_disable looks > very dangerous to me. raw_spin_lock_irq() disables irqs/preemption regardless of RT, task switch is not possible. > Do you know other places where such > a code pattern is used? For example, double_lock_irq(). See task_numa_group(), double_lock_irq(&my_grp->lock, &grp->lock); .... spin_unlock(&my_grp->lock); spin_unlock_irq(&grp->lock); this can unlock the locks in reverse order. I am sure there are more examples. > I do just ask, because a close look at those might reveal > some serious bugs, WDYT? See above, I don't understand your concerns... Oleg.