Re: [PATCH v3 31/35] lib: add memory allocations report in show_mem()

Tetsuo Handa
2024-02-21T13:24:35Z

On 2024/02/21 3:27, Vlastimil Babka wrote:
> I'm sure more such scenarios exist, Cc: Tetsuo who I recall was an expert on
> this topic.

"[PATCH v3 10/35] lib: code tagging framework" says that codetag_lock_module_list()
calls down_read() (i.e. sleeping operation), and
"[PATCH v3 31/35] lib: add memory allocations report in show_mem()" says that
__show_mem() calls alloc_tags_show_mem_report() after kmalloc(GFP_ATOMIC) (i.e.
non-sleeping operation) but alloc_tags_show_mem_report() calls down_read() via
codetag_lock_module_list() !?

If __show_mem() might be called from atomic context (e.g. kmalloc(GFP_ATOMIC)),
this will be a sleep in atomic bug.
If __show_mem() might be called while semaphore is held for write,
this will be a read-lock after write-lock deadlock bug.

Not the matter of whether to allocate buffer statically or dynamically.
Please don't hold a lock when trying to report memory usage.