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b=h1WPTm/7QlbvpxONpZIjyQnpJr6EYMV7k2vo7US6F0HAY4IArxzBTGL7BWC/X0XGj 9bNX81UbibUZo0CqTQptZWXTyogqqcq1VvMllbSjGKMZV0ejjZ460LuerJVLdwwY/T 74PAP8PWrie/s6nHPH6KSpGaff6DD3DHTtaA053lf2fB/juXjq13WQh5JHOoU+51mm 3soWU4q0jEgU01GZ5xgUlNVDpWrcoadEihit/OUTmjbBt/vZ9DAHvbbeh310IyeFdo ENOTUXZ+vvq4OMeC7oMnQOsGl23ewtTJV70bYY/B8/DMKEGNGN+9G/PPtQr4Kigsk4 AMG0KIQIrCG7Q== From: "Harry Yoo (Oracle)" Date: Mon, 27 Apr 2026 16:09:53 +0900 Subject: [PATCH mm-hotfixes v2 2/2] mm/slab: return NULL early from kmalloc_nolock() in NMI on UP MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20260427-nolock-api-fix-v2-2-a6b83a92d9a4@kernel.org> References: <20260427-nolock-api-fix-v2-0-a6b83a92d9a4@kernel.org> In-Reply-To: <20260427-nolock-api-fix-v2-0-a6b83a92d9a4@kernel.org> To: Andrew Morton , Vlastimil Babka , Suren Baghdasaryan , Michal Hocko , Brendan Jackman , Johannes Weiner , Zi Yan , Harry Yoo , Shakeel Butt , Alexei Starovoitov , Hao Li , Christoph Lameter , David Rientjes , Roman Gushchin Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org X-Mailer: b4 0.16-dev X-Stat-Signature: b9ghxupfx8h3d88zynt1cwm753wweqtk X-Rspamd-Queue-Id: 58E121C000C X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1777273835-342990 X-HE-Meta: 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 APtJiPLe vwQTjKwOfV4wOBcdDJDcUEOWeb7Axk1Vm4Oxj3ANjjuWe4bLWXZGzLWSzCCBEYTe9vYApMmByHF4NJ1uCtQlFGmYZRa5SMX+plkBxOIQeLAfWPIjHGqKSNoaR3etO0YUd3FdOU4b/wJEM5h/w05E7cf11ScZUpOZxJsuTJ/Lkd8QPNij/XcyEAMM58+HwsYGJgp1gI81IzYpnJQj1zwVW/3+m6n8YvOMqM8p0YqfrVyYwFn03+YhiQ0GEdOLA5p0bsGMMwAKCSBITtWJHjVYk2nvbH0Rl8xRg0BZT Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On UP kernels (!CONFIG_SMP), spin_trylock() is a no-op that unconditionally succeeds even when the lock is already held. As a result, kmalloc_nolock() called from NMI context can re-enter the slab allocator and acquire n->list_lock that the interrupted context is already holding, corrupting slab state. With CONFIG_DEBUG_SPINLOCK on UP, the following BUG is triggered with the slub_kunit test module: BUG: spinlock trylock failure on UP on CPU#0, kunit_try_catch/243 [...] Call Trace: dump_stack_lvl+0x3f/0x60 do_raw_spin_trylock+0x41/0x50 _raw_spin_trylock+0x24/0x50 get_from_partial_node+0x120/0x4d0 ___slab_alloc+0x8a/0x4c0 kmalloc_nolock_noprof+0x164/0x310 [...] Fix this by returning NULL early when invoked from NMI on a UP kernel. Link: https://lore.kernel.org/linux-mm/ad_cqe51pvr1WaDg@hyeyoo Cc: Fixes: af92793e52c3 ("slab: Introduce kmalloc_nolock() and kfree_nolock().") Signed-off-by: Harry Yoo (Oracle) --- mm/slub.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/mm/slub.c b/mm/slub.c index 92362eeb13e5..b4ec15df92f6 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -5339,6 +5339,10 @@ void *kmalloc_nolock_noprof(size_t size, gfp_t gfp_flags, int node) if (IS_ENABLED(CONFIG_PREEMPT_RT) && (in_nmi() || in_hardirq())) return NULL; + /* On UP, spin_trylock() always succeeds even when it is locked */ + if (!IS_ENABLED(CONFIG_SMP) && in_nmi()) + return NULL; + retry: if (unlikely(size > KMALLOC_MAX_CACHE_SIZE)) return NULL; -- 2.43.0