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    SubjectRe: [PATCH] mm/vmalloc: allow mem_dump_obj() to be called in interrupt context
    On Sat, 12 Nov 2022 20:15:37 +0800 Zhen Lei <thunder.leizhen@huawei.com> wrote:

    > The function mem_dump_obj() can sometimes provide valuable debugging
    > information, but it cannot be called in an interrupt context because
    > spinlock vmap_area_lock has not been protected against IRQs. If the
    > current task has held the lock before hard/soft interrupt handler calls
    > mem_dump_obj(), simply abandoning the dump operation can avoid deadlock.
    > That is, no deadlock occurs in extreme cases, and dump succeeds in most
    > cases.
    >
    > ...
    >
    > --- a/mm/vmalloc.c
    > +++ b/mm/vmalloc.c
    > @@ -4034,6 +4034,9 @@ bool vmalloc_dump_obj(void *object)
    > struct vm_struct *vm;
    > void *objp = (void *)PAGE_ALIGN((unsigned long)object);
    >
    > + if (unlikely(spin_is_locked(&vmap_area_lock)))
    > + return false;
    > +
    > vm = find_vm_area(objp);
    > if (!vm)
    > return false;

    Yes, but this will worsen the current uses of this function. Consider
    the case where task A wants to call vmalloc_dump_obj() but task B holds
    vmap_area_lock. No problem, task A will simply spin until task B is
    done.

    But after this patch, task A's call to vmalloc_dump_obj() will return
    without having done anything.

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