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Mikhail Gavrilov
2fb552b0be
Booting with a boot-time function tracer and a filter, for example ftrace=function ftrace_filter=pud_free_pmd_page panics on 7.3-rc4 as soon as the tracer starts: [ 23.531178] Starting tracer 'function' [ 23.675800] Oops: general protection fault, probably for non-canonical address 0xdffffc0000000038: 0000 [#1] SMP KASAN NOPTI [ 23.819917] KASAN: null-ptr-deref in range [0x00000000000001c0-0x00000000000001c7] [ 23.964025] CPU: 0 UID: 0 PID: 0 Comm: swapper Not tainted 7.3.0-rc4-fe2ec83746e5-with-fixes-v2+ #195 PREEMPT(undef) [ 24.252248] RIP: 0010:__queue_work+0xab/0xf00 [ 25.981629] Call Trace: [ 26.125727] <TASK> [ 26.413912] ? pagetable_free_kernel+0x20/0x120 [ 26.990283] queue_work_on+0x97/0xf0 [ 27.134382] __cpa_collapse_large_pages+0x501/0x6f0 [ 27.566662] cpa_flush+0x394/0x620 [ 27.998953] change_page_attr_set_clr+0x321/0x4a0 [ 29.151729] set_memory_rox+0xa2/0xf0 [ 29.584018] create_trampoline+0x431/0x6f0 ... [ 44.343347] Kernel panic - not syncing: Attempted to kill the idle task! The boot-time tracer is started from early_trace_init(), which runs before workqueue_init_early(). Making its trampoline read-only splits a large page, and CPA collapses it again right away. The split table has been a kernel page table since commit9e4a3ec341("x86/mm/pat: Allocate split page tables as kernel page tables"), so the collapse frees it through pagetable_free_kernel(), which queues work on system_percpu_wq - still NULL at that point. That commit is correct in itself; it only lets CPA reach pagetable_free_kernel() before the workqueue that function relies on exists. Keep putting the table on the list, but don't schedule the work while the system is still booting. A core_initcall schedules it once to free whatever was queued by then. Link: https://lore.kernel.org/20260925050647.86913-1-mikhail.v.gavrilov@gmail.com Link: https://lore.kernel.org/20260924064321.23787-1-mikhail.v.gavrilov@gmail.com Fixes:9e4a3ec341("x86/mm/pat: Allocate split page tables as kernel page tables") Signed-off-by: Mikhail Gavrilov <mikhail.v.gavrilov@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Suggested-by: David Hildenbrand (Arm) <david@kernel.org> Suggested-by: Lorenzo Stoakes (ARM) <ljs@kernel.org> Reviewed-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: David Hildenbrand (Arm) <david@kernel.org> Reviewed-by: Lorenzo Stoakes (ARM) <ljs@kernel.org> Reviewed-by: Jose A. Perez de Azpillaga <azpijr@gmail.com> Tested-by: Jose A. Perez de Azpillaga <azpijr@gmail.com> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: Liam R. Howlett <liam@infradead.org> Cc: Vlastimil Babka <vbabka@kernel.org> Cc: Mike Rapoport <rppt@kernel.org> Cc: Suren Baghdasaryan <surenb@google.com> Cc: Michal Hocko <mhocko@suse.com> Cc: Vishal Moola (Oracle) <vishal.moola@gmail.com> Cc: Ingo Molnar <mingo@kernel.org> Cc: Lu Baolu <baolu.lu@linux.intel.com> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: <stable@vger.kernel.org>