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Commit9a5b183941("mm, percpu: do not consider sleepable allocations atomic") allows sleepable GFP_NOIO and GFP_NOFS percpu allocations to take pcpu_alloc_mutex. This avoids premature allocation failures, but it also makes the mutex visible to callers from constrained IO/FS contexts. Thread A calls pcpu_alloc_noprof() with GFP_KERNEL and takes pcpu_alloc_mutex. Since the internal allocation is not constrained by NOFS, it may enter FS reclaim while still holding pcpu_alloc_mutex, creating a dependency like: pcpu_alloc_mutex -> fs_reclaim -> FS lock At the same time, Thread B may already hold an FS lock and then call pcpu_alloc_noprof() with GFP_NOFS. It will try to acquire pcpu_alloc_mutex and block, creating the reverse dependency: FS lock -> pcpu_alloc_mutex This can still form a potential deadlock cycle. Avoid the dependency by restricting percpu backing allocations to GFP_NOIO. The public allocation still uses the caller's GFP context to decide whether it may block, but the internal memory allocations performed while pcpu_alloc_mutex is held cannot recurse into IO or FS reclaim. Link: https://lore.kernel.org/20260618130414.96383-5-kaitao.cheng@linux.dev Fixes:9a5b183941("mm, percpu: do not consider sleepable allocations atomic") Signed-off-by: Kaitao Cheng <chengkaitao@kylinos.cn> Cc: Christoph Lameter <cl@gentwo.org> Cc: Dennis Zhou <dennis@kernel.org> Cc: Michal Hocko <mhocko@suse.com> Cc: Pedro Falcato <pfalcato@suse.de> Cc: Shivam Kalra <shivamkalra98@zohomail.in> Cc: Tejun Heo <tj@kernel.org> Cc: Uladzislau Rezki (Sony) <urezki@gmail.com> Cc: Vlastimil Babka <vbabka@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
3396 lines
101 KiB
3396 lines
101 KiB