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The ancient comment above task_lock() states that it can be nested outside of read_lock(&tasklist_lock), but this is no longer true: CPU_0 CPU_1 CPU_2 task_lock() read_lock(tasklist) write_lock_irq(tasklist) read_lock(tasklist) task_lock() Unless CPU_0 calls read_lock() in IRQ context, queued_read_lock_slowpath() won't get the lock immediately, it will spin waiting for the pending writer on CPU_2, resulting in a deadlock. Link: https://lkml.kernel.org/r/20250914110908.GA18769@redhat.com Signed-off-by: Oleg Nesterov <oleg@redhat.com> Cc: Christian Brauner <brauner@kernel.org> Cc: Jiri Slaby <jirislaby@kernel.org> Cc: Mateusz Guzik <mjguzik@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>