mm: don't schedule deferred kernel page table freeing while booting

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 commit 9e4a3ec3411b
("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: 9e4a3ec3411b ("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>

0 files changed, 0 insertions, 0 deletions