linux-kernel - Re: [PATCH 34/40] lib: code tagging context capture support

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Message-ID: <ZFIO3tXCbmTn53uv@dhcp22.suse.cz>
Date:   Wed, 3 May 2023 09:35:58 +0200
From:   Michal Hocko <mhocko@...e.com>
To:     Suren Baghdasaryan <surenb@...gle.com>
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Subject: Re: [PATCH 34/40] lib: code tagging context capture support

On Mon 01-05-23 09:54:44, Suren Baghdasaryan wrote:
[...]
> +static inline void add_ctx(struct codetag_ctx *ctx,
> +			   struct codetag_with_ctx *ctc)
> +{
> +	kref_init(&ctx->refcount);
> +	spin_lock(&ctc->ctx_lock);
> +	ctx->flags = CTC_FLAG_CTX_PTR;
> +	ctx->ctc = ctc;
> +	list_add_tail(&ctx->node, &ctc->ctx_head);
> +	spin_unlock(&ctc->ctx_lock);

AFAIU every single tracked allocation will get its own codetag_ctx.
There is no aggregation per allocation site or anything else. This looks
like a scalability and a memory overhead red flag to me.

> +}
> +
> +static inline void rem_ctx(struct codetag_ctx *ctx,
> +			   void (*free_ctx)(struct kref *refcount))
> +{
> +	struct codetag_with_ctx *ctc = ctx->ctc;
> +
> +	spin_lock(&ctc->ctx_lock);

This could deadlock when allocator is called from the IRQ context.

> +	/* ctx might have been removed while we were using it */
> +	if (!list_empty(&ctx->node))
> +		list_del_init(&ctx->node);
> +	spin_unlock(&ctc->ctx_lock);
> +	kref_put(&ctx->refcount, free_ctx);
-- 
Michal Hocko
SUSE Labs