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Content-Language: en-US To: Alexei Starovoitov , bpf@vger.kernel.org, linux-mm@kvack.org Cc: harry.yoo@oracle.com, shakeel.butt@linux.dev, mhocko@suse.com, bigeasy@linutronix.de, andrii@kernel.org, memxor@gmail.com, akpm@linux-foundation.org, peterz@infradead.org, rostedt@goodmis.org, hannes@cmpxchg.org References: <20250709015303.8107-1-alexei.starovoitov@gmail.com> <20250709015303.8107-7-alexei.starovoitov@gmail.com> From: Vlastimil Babka Autocrypt: addr=vbabka@suse.cz; keydata= xsFNBFZdmxYBEADsw/SiUSjB0dM+vSh95UkgcHjzEVBlby/Fg+g42O7LAEkCYXi/vvq31JTB KxRWDHX0R2tgpFDXHnzZcQywawu8eSq0LxzxFNYMvtB7sV1pxYwej2qx9B75qW2plBs+7+YB 87tMFA+u+L4Z5xAzIimfLD5EKC56kJ1CsXlM8S/LHcmdD9Ctkn3trYDNnat0eoAcfPIP2OZ+ 9oe9IF/R28zmh0ifLXyJQQz5ofdj4bPf8ecEW0rhcqHfTD8k4yK0xxt3xW+6Exqp9n9bydiy tcSAw/TahjW6yrA+6JhSBv1v2tIm+itQc073zjSX8OFL51qQVzRFr7H2UQG33lw2QrvHRXqD Ot7ViKam7v0Ho9wEWiQOOZlHItOOXFphWb2yq3nzrKe45oWoSgkxKb97MVsQ+q2SYjJRBBH4 8qKhphADYxkIP6yut/eaj9ImvRUZZRi0DTc8xfnvHGTjKbJzC2xpFcY0DQbZzuwsIZ8OPJCc LM4S7mT25NE5kUTG/TKQCk922vRdGVMoLA7dIQrgXnRXtyT61sg8PG4wcfOnuWf8577aXP1x 6mzw3/jh3F+oSBHb/GcLC7mvWreJifUL2gEdssGfXhGWBo6zLS3qhgtwjay0Jl+kza1lo+Cv BB2T79D4WGdDuVa4eOrQ02TxqGN7G0Biz5ZLRSFzQSQwLn8fbwARAQABzSBWbGFzdGltaWwg QmFia2EgPHZiYWJrYUBzdXNlLmN6PsLBlAQTAQoAPgIbAwULCQgHAwUVCgkICwUWAgMBAAIe AQIXgBYhBKlA1DSZLC6OmRA9UCJPp+fMgqZkBQJnyBr8BQka0IFQAAoJECJPp+fMgqZkqmMQ AIbGN95ptUMUvo6aAdhxaOCHXp1DfIBuIOK/zpx8ylY4pOwu3GRe4dQ8u4XS9gaZ96Gj4bC+ jwWcSmn+TjtKW3rH1dRKopvC07tSJIGGVyw7ieV/5cbFffA8NL0ILowzVg8w1ipnz1VTkWDr 2zcfslxJsJ6vhXw5/npcY0ldeC1E8f6UUoa4eyoskd70vO0wOAoGd02ZkJoox3F5ODM0kjHu Y97VLOa3GG66lh+ZEelVZEujHfKceCw9G3PMvEzyLFbXvSOigZQMdKzQ8D/OChwqig8wFBmV QCPS4yDdmZP3oeDHRjJ9jvMUKoYODiNKsl2F+xXwyRM2qoKRqFlhCn4usVd1+wmv9iLV8nPs 2Db1ZIa49fJet3Sk3PN4bV1rAPuWvtbuTBN39Q/6MgkLTYHb84HyFKw14Rqe5YorrBLbF3rl M51Dpf6Egu1yTJDHCTEwePWug4XI11FT8lK0LNnHNpbhTCYRjX73iWOnFraJNcURld1jL1nV r/LRD+/e2gNtSTPK0Qkon6HcOBZnxRoqtazTU6YQRmGlT0v+rukj/cn5sToYibWLn+RoV1CE Qj6tApOiHBkpEsCzHGu+iDQ1WT0Idtdynst738f/uCeCMkdRu4WMZjteQaqvARFwCy3P/jpK uvzMtves5HvZw33ZwOtMCgbpce00DaET4y/UzsBNBFsZNTUBCACfQfpSsWJZyi+SHoRdVyX5 J6rI7okc4+b571a7RXD5UhS9dlVRVVAtrU9ANSLqPTQKGVxHrqD39XSw8hxK61pw8p90pg4G /N3iuWEvyt+t0SxDDkClnGsDyRhlUyEWYFEoBrrCizbmahOUwqkJbNMfzj5Y7n7OIJOxNRkB IBOjPdF26dMP69BwePQao1M8Acrrex9sAHYjQGyVmReRjVEtv9iG4DoTsnIR3amKVk6si4Ea X/mrapJqSCcBUVYUFH8M7bsm4CSxier5ofy8jTEa/CfvkqpKThTMCQPNZKY7hke5qEq1CBk2 wxhX48ZrJEFf1v3NuV3OimgsF2odzieNABEBAAHCwXwEGAEKACYCGwwWIQSpQNQ0mSwujpkQ PVAiT6fnzIKmZAUCZ8gcVAUJFhTonwAKCRAiT6fnzIKmZLY8D/9uo3Ut9yi2YCuASWxr7QQZ lJCViArjymbxYB5NdOeC50/0gnhK4pgdHlE2MdwF6o34x7TPFGpjNFvycZqccSQPJ/gibwNA zx3q9vJT4Vw+YbiyS53iSBLXMweeVV1Jd9IjAoL+EqB0cbxoFXvnjkvP1foiiF5r73jCd4PR rD+GoX5BZ7AZmFYmuJYBm28STM2NA6LhT0X+2su16f/HtummENKcMwom0hNu3MBNPUOrujtW khQrWcJNAAsy4yMoJ2Lw51T/5X5Hc7jQ9da9fyqu+phqlVtn70qpPvgWy4HRhr25fCAEXZDp xG4RNmTm+pqorHOqhBkI7wA7P/nyPo7ZEc3L+ZkQ37u0nlOyrjbNUniPGxPxv1imVq8IyycG AN5FaFxtiELK22gvudghLJaDiRBhn8/AhXc642/Z/yIpizE2xG4KU4AXzb6C+o7LX/WmmsWP Ly6jamSg6tvrdo4/e87lUedEqCtrp2o1xpn5zongf6cQkaLZKQcBQnPmgHO5OG8+50u88D9I rywqgzTUhHFKKF6/9L/lYtrNcHU8Z6Y4Ju/MLUiNYkmtrGIMnkjKCiRqlRrZE/v5YFHbayRD dJKXobXTtCBYpLJM4ZYRpGZXne/FAtWNe4KbNJJqxMvrTOrnIatPj8NhBVI0RSJRsbilh6TE m6M14QORSWTLRg== In-Reply-To: <20250709015303.8107-7-alexei.starovoitov@gmail.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 462A7C0012 X-Stat-Signature: y3c3ybjx7zjwr9ars4ncmdyi4jibeebn X-HE-Tag: 1752140164-952747 X-HE-Meta: U2FsdGVkX19NeeQ1Ar50jE9vLfQg8PY9sdH1jxfad5R69oJqbUBKH28uljoCMft+t1jAV6pE3MLpNPMUmehQVdTKAz4xed90U0eYTdYBvy3JoUrhv2rf70I68IbSPF4gg3Qk/TV1oJKd8yCOz7pz7xddxUGigauOYpsjJl0cv/WUGllROQ9wtZsiklvOHqvEvITAj+3XMd4Bac6YATMSPLfquPp0pPsdFZnNmSGhD+q66/8EwjtTIAvIgF4UghcGxdtYK785MtIIGfX4eLpdQOl7RYAjjA1eTDULRio+7lROtRDYzcYW21GGBFWVMUReXujEJLLx1jffidDG6ORgjRpbAPwagpE9Hquptj0oHS0gzcWe/Awz7EJCaNnl8RSR86F+1k0PRjV4hxGg2XIfW4fGwfOXXZgXhTIF7ZqU0rYXEw2gV4i0hIbQbDQRDwKAF5JvaanezM6MMNaKLKFqFX4RTY4Qw6rIFdFzNPr2WL2BU32okgMQQDmfPFXDMytZLvBImRrIlS/K9Zljpo3Mwc/hD5KPrchA6YWwaNu2fUjBqp8C9PptzvlPjTguq4SbyT2OPkYrpq/ghZKA+uwIensYr+iXHeiO7pJuuonTr+XynzlrF6I6YUTSipvVC1m52J3FzAHztB4XR1y3FDRZXra7KSbBP+XtExytXcAejgdf+rRd2W5Wp9XdAPXigrUQnbos82g/1A74Q//aATVTZZ1E/jWiQIvI1IX4M0dh3Ylt679hFcGQkBrVMsuQEDmLPFfBgiu8rWtgxFjJcEagR32SFU/lGhas4T6wAQw9/4Fz+y9+Q4b8BcPhJwoaVJHy7St0z/QvpiYi9fa9/+SEZkFpsdtF5Cy6RpFplLUSJzFVI1NEGgANpu/ZN0Dp/bsNC4ZbqOP8803GZu43jev2sz0HjjQ0hWRTPExj9vW2krDgEcA6YBxO30/Q8plZiP6cbDB4IqeAn/YB7XKyLQD E9QChSvJ D2VcM9si6Qo+bwPQ3xAI4bIn76KHL1svsh8OgPdMo/5+kk/fCR51J71YQgsU4rvLi9fXvp2zyXtX2q2/8OI6gL9H+13R8bJpUcZTHuQORtDvUVFhpgH5UWBPRyzlMwR3WHo3EVXEmQ8br7uPb9CIwQ0E3f1tpUr+cxOQhjoMHs7qTNCN1/oSEPX9u8VhBnQpsOBnq3qwa9vfZlVT/SidqBusbUV7LEfrgiUiWbV/Ds2mVexsF5lTn12wRsUFvxm0CH4SPILjqlYEhnA1dN8bJ9OVhMCUxE08EH2HKx83+h+6yE4OFnFrpi/+R9E4qKCZs5tvCXPwxT8VN+h6UY8kLZ1CBHUALoD/o32KffMevcUWOin6W72+wGLQTEdpL+OQ3BNmVhyxxIBvE4dqykc2WEzKs+bMs+OOR/DwGZ7c8y6GcEso= 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 7/9/25 03:53, Alexei Starovoitov wrote: > From: Alexei Starovoitov > > kmalloc_nolock() relies on ability of local_lock to detect the situation > when it's locked. > In !PREEMPT_RT local_lock_is_locked() is true only when NMI happened in > irq saved region that protects _that specific_ per-cpu kmem_cache_cpu. > In that case retry the operation in a different kmalloc bucket. > The second attempt will likely succeed, since this cpu locked > different kmem_cache_cpu. > > Similarly, in PREEMPT_RT local_lock_is_locked() returns true when > per-cpu rt_spin_lock is locked by current task. In this case re-entrance > into the same kmalloc bucket is unsafe, and kmalloc_nolock() tries > a different bucket that is most likely is not locked by the current > task. Though it may be locked by a different task it's safe to > rt_spin_lock() on it. > > Similar to alloc_pages_nolock() the kmalloc_nolock() returns NULL > immediately if called from hard irq or NMI in PREEMPT_RT. > > kfree_nolock() defers freeing to irq_work when local_lock_is_locked() > and in_nmi() or in PREEMPT_RT. > > SLUB_TINY config doesn't use local_lock_is_locked() and relies on > spin_trylock_irqsave(&n->list_lock) to allocate while kfree_nolock() > always defers to irq_work. > > Signed-off-by: Alexei Starovoitov > static __fastpath_inline > @@ -2442,13 +2453,17 @@ static void *setup_object(struct kmem_cache *s, void *object) > * Slab allocation and freeing > */ > static inline struct slab *alloc_slab_page(gfp_t flags, int node, > - struct kmem_cache_order_objects oo) > + struct kmem_cache_order_objects oo, > + bool allow_spin) > { > struct folio *folio; > struct slab *slab; > unsigned int order = oo_order(oo); > > - if (node == NUMA_NO_NODE) > + if (unlikely(!allow_spin)) { > + folio = (struct folio *)alloc_frozen_pages_nolock(0/* __GFP_COMP is implied */, > + node, order); > + } else if (node == NUMA_NO_NODE) > folio = (struct folio *)alloc_frozen_pages(flags, order); > else > folio = (struct folio *)__alloc_frozen_pages(flags, order, node, NULL); Nit: should use { } either for everything or nothing (seems your new branch would work without them) > stat(s, ALLOC_NODE_MISMATCH); > @@ -3730,7 +3762,7 @@ static void *___slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node, > * PFMEMALLOC but right now, we are losing the pfmemalloc > * information when the page leaves the per-cpu allocator > */ > - if (unlikely(!pfmemalloc_match(slab, gfpflags))) > + if (unlikely(!pfmemalloc_match(slab, gfpflags) && allow_spin)) > goto deactivate_slab; > > /* must check again c->slab in case we got preempted and it changed */ > @@ -3803,7 +3835,12 @@ static void *___slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node, > slub_set_percpu_partial(c, slab); > > if (likely(node_match(slab, node) && > - pfmemalloc_match(slab, gfpflags))) { > + pfmemalloc_match(slab, gfpflags)) || > + /* > + * Reentrant slub cannot take locks necessary > + * for __put_partials(), hence downgrade to any node > + */ > + !allow_spin) { Uh this seems rather ugly, I'd move the comment above everything. Also it's not "downgrade" as when you assign NUMA_NO_NODE earlier, I'd say "ignore the preference". Note that it would be bad to ignore with __GFP_THISNODE but then it's not allowed for kmalloc_nolock() so that's fine. > @@ -3911,6 +3953,12 @@ static void *___slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node, > void *flush_freelist = c->freelist; > struct slab *flush_slab = c->slab; > > + if (unlikely(!allow_spin)) > + /* > + * Reentrant slub cannot take locks > + * necessary for deactivate_slab() > + */ > + return NULL; Hm but this is leaking the slab we allocated and have in the "slab" variable, we need to free it back in that case. > c->slab = NULL; > c->freelist = NULL; > c->tid = next_tid(c->tid); > @@ -4593,10 +4792,31 @@ static __always_inline void do_slab_free(struct kmem_cache *s, > barrier(); > > if (unlikely(slab != c->slab)) { > - __slab_free(s, slab, head, tail, cnt, addr); > + /* cnt == 0 signals that it's called from kfree_nolock() */ > + if (unlikely(!cnt)) { > + /* > + * __slab_free() can locklessly cmpxchg16 into a slab, > + * but then it might need to take spin_lock or local_lock > + * in put_cpu_partial() for further processing. > + * Avoid the complexity and simply add to a deferred list. > + */ > + defer_free(head); > + } else { > + __slab_free(s, slab, head, tail, cnt, addr); > + } > return; > } > > + if (unlikely(!cnt)) { > + if ((in_nmi() || !USE_LOCKLESS_FAST_PATH()) && > + local_lock_is_locked(&s->cpu_slab->lock)) { > + defer_free(head); > + return; > + } > + cnt = 1; Hmm we might end up doing a "goto redo" later and then do the wrong thing above? > + kasan_slab_free(s, head, false, false, /* skip quarantine */true); > + } > + > if (USE_LOCKLESS_FAST_PATH()) { > freelist = READ_ONCE(c->freelist); >