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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Spamd-Result: default: False [-4.51 / 50.00]; BAYES_HAM(-3.00)[100.00%]; NEURAL_HAM_LONG(-1.00)[-1.000]; R_DKIM_ALLOW(-0.20)[suse.cz:s=susede2_rsa,suse.cz:s=susede2_ed25519]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; MX_GOOD(-0.01)[]; FUZZY_RATELIMITED(0.00)[rspamd.com]; RCVD_TLS_ALL(0.00)[]; ARC_NA(0.00)[]; RCVD_VIA_SMTP_AUTH(0.00)[]; MIME_TRACE(0.00)[0:+]; RCPT_COUNT_SEVEN(0.00)[10]; DKIM_SIGNED(0.00)[suse.cz:s=susede2_rsa,suse.cz:s=susede2_ed25519]; TO_DN_SOME(0.00)[]; FROM_HAS_DN(0.00)[]; MID_RHS_MATCH_FROM(0.00)[]; FROM_EQ_ENVFROM(0.00)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; DKIM_TRACE(0.00)[suse.cz:+] X-Spam-Flag: NO X-Spam-Score: -4.51 X-Rspamd-Queue-Id: BC146349B0 X-Rspamd-Action: no action X-Rspamd-Server: rspamd2.dmz-prg2.suse.org X-Spam-Level: On 1/13/26 12:55, Sebastian Andrzej Siewior wrote: > On 2026-01-12 12:14:30 [-0500], Waiman Long wrote: >> On 1/12/26 10:09 AM, Thomas Gleixner wrote: >> > They might be acquired though. Only alloc_pages_nolock() guarantees that >> > no lock is taken IIRC. >> >> Thanks for the suggestion. I will look into using that for page allocation. >> I had actually attempt to use kmalloc_nolock() to replace kzalloc() >> initially. Even though it removed the call to rmqueue(), but there were >> other spinlocks in the slub code that were still being acquired like the >> local_lock() or the spinlock in the get_random() code. So I gave up using Hmm if get_random() code takes a spinlock, we have an unsolved incompatibility with kmalloc_nolock() and CONFIG_SLAB_FREELIST_RANDOM. >> that. Anyway, kmalloc_nolock() doesn't seem to be fully working yet. > > with kmalloc_nolock() you have to be able to deal with a NULL pointer. Yes. So even after we fix the current problems with incompatible context, I think kmalloc_nolock() would still be a bad fit for hw bringup code that should not really fail. Because the possibility of failure will always exist. The BPF use case that motivated it is quite different. > Looking at kmalloc_nolock(), it has this (in_nmi() || in_hardirq()) > check on PREEMPT_RT. The reasoning was unconditional raw_spinlock_t > locking and bad lock-owner recording for hardirq. > There was a trylock path for local_lock to make it work from atomic > context. But from what I can tell this goes > kmalloc_nolock_noprof() -> __slab_alloc_node() -> __slab_alloc() -> > ___slab_alloc() -> local_lock_cpu_slab() > > The last one does local_lock_irqsave() on PREEMPT_RT which does a > spin_lock(). That means atomic context is not possible. Where did I make > a wrong turn? Or did this change recently? I do remember that Alexei > reworked parts of the allocator to make the local_lock based trylock > allocation work. > >> Cheers, >> Longman > > Sebastian