linux-kernel - Re: [PATCH] ref_tracker: add stack_depot_save() failure handling to ref_tracker

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Message-ID: <c17ff3ff-b3af-fea2-f75e-68cefbc90636@I-love.SAKURA.ne.jp>
Date:   Tue, 30 May 2023 18:51:32 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:     Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>
Cc:     Dmitry Vyukov <dvyukov@...gle.com>,
        "David S. Miller" <davem@...emloft.net>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ref_tracker: add stack_depot_save() failure handling to
 ref_tracker_alloc()

On 2023/05/30 16:22, Eric Dumazet wrote:
>>> Therefore, assume that stack_depot_save(GFP_KERNEL | __GFP_NOFAIL) from
>>> ref_tracker_alloc() can silently fail, and emit "unreliable refcount
>>> tracker." message.
>
> Note: I never assumed stack_depot_save() would enforce/use NOFAIL.

Hmm, I misread this function.

	if (gfp & __GFP_DIRECT_RECLAIM)
		gfp_mask |= __GFP_NOFAIL; // Or'ing to "gfp_mask" than "gfp".
	*trackerp = tracker = kzalloc(sizeof(*tracker), gfp_mask); // <= This is "gfp_mask".
	tracker->alloc_stack_handle = stack_depot_save(entries, nr_entries, gfp); // <= This is "gfp".

So, stack_depot_save(GFP_KERNEL | __GFP_NOFAIL) is not happening.

Then, question becomes whether we want tracker->alloc_stack_handle != NULL or not.
If tracker->alloc_stack_handle == NULL is still useful, this patch will be useless...