mm/page_alloc: don't spin_trylock() in NMI on UP

Patch series "mm/page_alloc: fixes for free_pages_nolock() on RT/UP".

Pre-existing bugs found by Sashiko during review of this other series:
https://lore.kernel.org/all/20260703-alloc-trylock-v5-0-c87b714e19d3@google.com/

I have not reproduced these bugs, and I suspect there is no real-world
user that is affected by them.


This patch (of 2):

As noted in can_spin_trylock(), using this is unsafe in this context. 
commit 620b46ed6ae17 ("mm/page_alloc: return NULL early from
alloc_frozen_pages_nolock() in NMI on UP") fixed this on the alloc side
but missed the free side.

Impact: If BPF programs using these features in NMI (probably tracing) are
present on non-SMP builds this might crash the kernel and is probably
exploitable by local attackers for privilege escalation.

Link: https://lore.kernel.org/20260715-alloc-nolock-fixes-v1-0-fadc49952dda@google.com
Link: https://lore.kernel.org/20260715-alloc-nolock-fixes-v1-1-fadc49952dda@google.com
Fixes: 8c57b687e833 ("mm, bpf: Introduce free_pages_nolock()")
Signed-off-by: Brendan Jackman <jackmanb@google.com>
Reported-by: sashiko-bot@kernel.org
Closes: https://sashiko.dev/#/patchset/20260703-alloc-trylock-v5-0-c87b714e19d3%40google.com?part=18
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>

0 files changed, 0 insertions, 0 deletions