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mm/page_alloc: don't spin_trylock() when disallowed in free_one_page()

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__free_frozen_pages() checks can_spin_trylock() before entering into the
main free_frozen_page_commit()/free_one_page() path, but before this it
can get to free_one_page() via the !pcp_allowed_order() and
MIGRATE_ISOLATE paths.

The !pcp_allowed_order() path depends on usage by callers so might not be
possible in practice.  The MIGRATE_ISOLATE path probably means kernel
crashes and privilege escalation if anyone ever did memory hotplug and BPF
tracing on a PREEMPT_RT or !SMP build.

Link: https://lore.kernel.org/20260715-alloc-nolock-fixes-v1-2-fadc49952dda@google.com
Signed-off-by: Brendan Jackman <jackmanb@google.com>
Fixes: 8c57b687e8 ("mm, bpf: Introduce free_pages_nolock()")
Reported-by: sashiko-bot@kernel.org
Closes: https://sashiko.dev/#/patchset/20260710-spin-trylock-followup-v1-0-affb5fe5ed00%40google.com?part=2
Reviewed-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>
Reviewed-by: Harry Yoo (Oracle) <harry@kernel.org>
Cc: Brendan Jackman <brendan.jackman@linux.dev>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Zi Yan <ziy@nvidia.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Brendan Jackman 2026-07-15 09:03:59 +00:00 committed by Andrew Morton
parent 3105ae628f
commit 52dcc33881
1 changed files with 1 additions and 1 deletions
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2
mm/page_alloc.c
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@ -1559,7 +1559,7 @@ static void free_one_page(struct zone *zone, struct page *page,
unsigned long flags;
if (unlikely(fpi_flags & FPI_TRYLOCK)) {
if (!spin_trylock_irqsave(&zone->lock, flags)) {
if (!can_spin_trylock() || !spin_trylock_irqsave(&zone->lock, flags)) {
add_page_to_zone_llist(zone, page, order);
return;
}