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Date:   Tue, 10 Apr 2018 13:06:33 +0200
From:   Oleg Nesterov <oleg@redhat.com>
To:     Ravi Bangoria <ravi.bangoria@linux.vnet.ibm.com>
Cc:     mhiramat@kernel.org, peterz@infradead.org,
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Subject: Re: [PATCH v2 7/9] trace_uprobe/sdt: Fix multiple update of same
 reference counter
Message-ID: <20180410110633.GA29063@redhat.com>
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 <84c1e60f-8aad-a0ce-59af-4fcb3f77df94@linux.vnet.ibm.com>
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Hi Ravi,

On 04/10, Ravi Bangoria wrote:
>
> > and what if __mmu_notifier_register() fails simply because signal_pending() == T?
> > see mm_take_all_locks().
> >
> > at first glance this all look suspicious and sub-optimal,
>
> Yes. I should have added checks for failure cases.
> Will fix them in v3.

And what can you do if it fails? Nothing except report the problem. But
signal_pending() is not the unlikely or error condition, it should not
cause the tracing errors.

Plus mm_take_all_locks() is very heavy... BTW, uprobe_mmap_callback() is
called unconditionally. Whatever it does, can we at least move it after
the no_uprobe_events() check? Can't we also check MMF_HAS_UPROBES?

Either way, I do not feel that mmu_notifier is the right tool... Did you
consider the uprobe_clear_state() hook we already have?

Oleg.