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Mon, 12 Jan 2026 20:09:14 +0800 (CST) X-Sender: hdanton@sina.com X-Auth-ID: hdanton@sina.com X-SMAIL-MID: 7763946291959 X-SMAIL-UIID: 0345F1A97CE046EA83CE27B384789124-20260112-200914-1 From: Hillf Danton To: Deepanshu Kartikey Cc: Uladzislau Rezki , akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com, syzbot+d8d4c31d40f868eaea30@syzkaller.appspotmail.com Subject: Re: [PATCH v2] mm/vmalloc: prevent RCU stalls in kasan_release_vmalloc_node Date: Mon, 12 Jan 2026 20:08:42 +0800 Message-ID: <20260112120904.2172-1-hdanton@sina.com> In-Reply-To: <20260112103612.627247-1-kartikey406@gmail.com> References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: C3F12180002 X-Stat-Signature: z5r6f18mci6ssk7ar6xewywj33dndnww X-Rspam-User: X-HE-Tag: 1768219759-429891 X-HE-Meta: U2FsdGVkX192s8V/Y8zTP+s1pVevrdyUhx2Q9qgYp5Y5kKC5kJPx/kTfkncaIHe8sRkhAl/LU63LaAzTNmueN1nZ8fOI1rsWMRYE0vTOTuaWmaRWH7hI4iezic0+M5u0cnTdiyMV7kERA9WY+u6hRTzq67m5C8YB8ruIRFS4LEnnk24HG8lz2xCQ74x4tY2vUQ5sy1+AruDNeScNCdWHG/V6pVNcIKIEzRd+mWodCPjwVQTrut8RA3kLWMZNesH6ayNMaYRtf3916WM9vWAdVo7obLo8x2itbmDxfedSlnMBnqcr5lmf8+tG9x6gDlsKSOM+pFSrnL+vO0PceOQ0NjBCtcbRezwHVqjeyVn73KpkqaWnJNSKZE4nHAXcO9AHkV/r6m/3dk86dFg9ZJ0zuJQf37XbLOG83+kEz7tUzxkLTTrp/4hkK7OEO6zJTUR+nv/i4rkHD0IxTyPH3wz8iGYII3eEJ1isdfpzlKlovIAv7L86UZW73+pOncUuGYQJEv6tzWLbnaTPMkXG3dTtqFMwF8TYNQ6wPPuB1nIX5zWT5DwikEcKSt26cav0awXkjwYeaDh6W7YrOf1M3saixC0kduVhjy+AUdLO5RE/40gVEA8qFbHIJFaftMbZtk1/oW4U410D6wVK29ArkYGFteQ5SHLbJjC4dF41XJtaqDcn4TdgDJFDMXJBTNui0DsDytQ1D2S0zbX9wVdO0STtzIAqc1jdYNejByDj6bRdeZ+FGpbnTJXMvgVmtESIoPCCDcnJvTjVMwG3ij/bhP5G7vH73NquqQwJg5bN+74vO7fl5BqQtrurv27QW4pamH//pSv173RDyuxRh4DkFrjK9xwtW6QF/pOYVsMSRcjCWc6XcYGmMNy5z4HZmFU3nc5YktR6/mMIPhHtqVnvpxX+773sswAIFcVm2kaIronaTuCGXoSsqi8finX3T7T25id63VJ6CCdZdd07Jff11Ng ck72wbwK 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 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: #syz test When CONFIG_PAGE_OWNER is enabled, freeing KASAN shadow pages during vmalloc cleanup triggers expensive stack unwinding that acquires RCU read locks. Processing a large purge_list without rescheduling can cause the task to hold CPU for extended periods (10+ seconds), leading to RCU stalls and potential OOM conditions. The issue manifests in purge_vmap_node() -> kasan_release_vmalloc_node() where iterating through hundreds or thousands of vmap_area entries and freeing their associated shadow pages causes: rcu: INFO: rcu_preempt detected stalls on CPUs/tasks: rcu: Tasks blocked on level-0 rcu_node (CPUs 0-1): P6229/1:b..l ... task:kworker/0:17 state:R running task stack:28840 pid:6229 ... kasan_release_vmalloc_node+0x1ba/0xad0 mm/vmalloc.c:2299 purge_vmap_node+0x1ba/0xad0 mm/vmalloc.c:2299 Each call to kasan_release_vmalloc() can free many pages, and with page_owner tracking, each free triggers save_stack() which performs stack unwinding under RCU read lock. Without yielding, this creates an unbounded RCU critical section. Add periodic cond_resched() calls within the loop to allow: - RCU grace periods to complete - Other tasks to run - Scheduler to preempt when needed The fix uses need_resched() for immediate response under load, with a batch count of 32 as a guaranteed upper bound to prevent worst-case stalls even under light load. Reported-by: syzbot+d8d4c31d40f868eaea30@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=d8d4c31d40f868eaea30 Link: https://lore.kernel.org/all/20260112084723.622910-1-kartikey406@gmail.com/T/ [v1] Suggested-by: Uladzislau Rezki Signed-off-by: Deepanshu Kartikey --- v2: Use a macro for batch size (suggested by Uladzislau Rezki) --- mm/vmalloc.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/mm/vmalloc.c b/mm/vmalloc.c index 41dd01e8430c..51e58701565d 100644 --- a/mm/vmalloc.c +++ b/mm/vmalloc.c @@ -2268,11 +2268,14 @@ decay_va_pool_node(struct vmap_node *vn, bool full_decay) reclaim_list_global(&decay_list); } +#define KASAN_RELEASE_BATCH_SIZE 32 + static void kasan_release_vmalloc_node(struct vmap_node *vn) { struct vmap_area *va; unsigned long start, end; + unsigned int batch_count = 0; start = list_first_entry(&vn->purge_list, struct vmap_area, list)->va_start; end = list_last_entry(&vn->purge_list, struct vmap_area, list)->va_end; @@ -2282,6 +2285,11 @@ kasan_release_vmalloc_node(struct vmap_node *vn) kasan_release_vmalloc(va->va_start, va->va_end, va->va_start, va->va_end, KASAN_VMALLOC_PAGE_RANGE); + + if (need_resched() || (++batch_count >= KASAN_RELEASE_BATCH_SIZE)) { + cond_resched(); + batch_count = 0; + } } kasan_release_vmalloc(start, end, start, end, KASAN_VMALLOC_TLB_FLUSH); -- 2.43.0