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 9e4a3ec341
("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/[email protected]
Link: https://lore.kernel.org/[email protected]
Fixes: 9e4a3ec341 ("x86/mm/pat: Allocate split page tables as kernel page tables")
Signed-off-by: Mikhail Gavrilov <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Suggested-by: David Hildenbrand (Arm) <[email protected]>
Suggested-by: Lorenzo Stoakes (ARM) <[email protected]>
Reviewed-by: Andrew Morton <[email protected]>
Reviewed-by: David Hildenbrand (Arm) <[email protected]>
Reviewed-by: Lorenzo Stoakes (ARM) <[email protected]>
Reviewed-by: Jose A. Perez de Azpillaga <[email protected]>
Tested-by: Jose A. Perez de Azpillaga <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: Liam R. Howlett <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Cc: Mike Rapoport <[email protected]>
Cc: Suren Baghdasaryan <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Vishal Moola (Oracle) <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Lu Baolu <[email protected]>
Cc: Jason Gunthorpe <[email protected]>
Cc: Steven Rostedt <[email protected]>
Cc: <[email protected]>
Mikhail Gavrilov
2fb552b0be