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Peter Zijlstra
c69df06e4e
Ian noted that commit77de62ad3d("perf/core: Fix refcount bug and potential UAF in perf_mmap") would cause a deadlock due to event->mmap_mutex recursion. This happens because we're now calling perf_mmap_close() under mmap_mutex, while that function itself can also take mmap_mutex. Solve this by noting that perf_mmap_close() is far more complicated than we need at this particular point, since it deals with scenarios that cannot happen in this particular case. Replace the call to perf_mmap_close() with a very narrow undo for the case of first-exposure. If this is not the first mmap(), there is no race and it is fine to drop the lock and call perf_mmap_close() to handle to more complicated scenarios. Note: move the rb->mmap_user (namespace) handling into the rb init/free code such that it does not complicate the mmap handling. Fixes:77de62ad3d("perf/core: Fix refcount bug and potential UAF in perf_mmap") Reported-by: Ian Rogers <[email protected]> Closes: https://patch.msgid.link/CAP-5%3DfVJyVMZw%3DDqP53Kxg58nUmJ_0bxoaeOKAbC03BVc11HaA%40mail.gmail.com Signed-off-by: Peter Zijlstra (Intel) <[email protected]> Link: https://patch.msgid.link/[email protected]