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Fri, 26 Dec 2025 15:53:32 -0800 (PST) MIME-Version: 1.0 References: <20251226184111.254674-1-sj@kernel.org> In-Reply-To: <20251226184111.254674-1-sj@kernel.org> From: JaeJoon Jung Date: Sat, 27 Dec 2025 08:53:21 +0900 X-Gm-Features: AQt7F2qKCfyxqagV7UlDOzpbncHuGGXw7tVVuiMUC6LDgDSt7Cv44S0l7SIN9po Message-ID: Subject: Re: [PATCH] mm/damon/sysfs: preventing duplicated list_add_tail() at the damon_call() To: SeongJae Park Cc: damon@lists.linux.dev, linux-mm@kvack.org, rgbi3307@nate.com Content-Type: text/plain; charset="UTF-8" X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: DFD4440005 X-Stat-Signature: ifn53yquezkoyunde3j4osi3o811hh1g X-Rspam-User: X-HE-Tag: 1766793213-120292 X-HE-Meta: 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 y5FKKg2j jqMuWYzvcv4U39VIzuoOwfiGXj9OltQwsYCbI+dgdVJeNcEsqu+EH+LRMYvW0sWMckap/nkIgd8jXeo5/czEXT8rMu/6E1eXcy9UbBVJRzRUodl/Lu3pxTE2BEarvNMOUix36hJ0NRM/s+oweAtj9xiYDKUgd2axkYMwRtWFQtmtg69WL6Zwm9BKuxzeaPxXhbUqGZumrpFiibiIPm9YKOlv0yLdeW1LfsaF94DdqvzYSn7wD5tpw/pLCKVFp2828ElbUskTeNvgoc9420U0EZ58UOIQsLpb0NbBTIzXqtXAp4VJ+u2M6CnpbyTrPtSVkOM8E/uh3lNjTEJcEqlFlunbVBLNVJeWJUxbfMyNKvnMjP9yCUNCg1toz3VzwRe8CFqVsqZDOWaK+CmxlcBvLEDwWkuMdTiFdeACYccwZB8OaDcOxOZ2EhUcMLVxGJaWah672 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Sat, 27 Dec 2025 at 03:41, SeongJae Park wrote: > > On Fri, 26 Dec 2025 10:48:31 +0900 JaeJoon Jung wrote: > > > On Fri, 26 Dec 2025 at 04:50, SeongJae Park wrote: > > > > > > On Thu, 25 Dec 2025 11:35:33 +0900 JaeJoon Jung wrote: > > > > > > > On Thu, 25 Dec 2025 at 09:32, SeongJae Park wrote: > > > > > > > > > > Hello JaeJoon, > > > > > > > > > > On Wed, 24 Dec 2025 18:43:58 +0900 JaeJoon Jung wrote: > [...] > > > > diff --git a/mm/damon/core.c b/mm/damon/core.c > > > > index babad37719b6..2ead0bb3c462 100644 > > > > --- a/mm/damon/core.c > > > > +++ b/mm/damon/core.c > > > > @@ -1462,6 +1462,9 @@ bool damon_is_running(struct damon_ctx *ctx) > > > > */ > > > > int damon_call(struct damon_ctx *ctx, struct damon_call_control *control) > > > > { > > > > + if (!damon_is_running(ctx)) > > > > + return -EINVAL; > > > > + > > > > if (!control->repeat) > > > > init_completion(&control->completion); > > > > control->canceled = false; > > > > @@ -1470,8 +1473,6 @@ int damon_call(struct damon_ctx *ctx, struct > > > > damon_call_control *control) > > > > mutex_lock(&ctx->call_controls_lock); > > > > list_add_tail(&control->list, &ctx->call_controls); > > > > mutex_unlock(&ctx->call_controls_lock); > > > > - if (!damon_is_running(ctx)) > > > > - return -EINVAL; > > > > if (control->repeat) > > > > return 0; > > > > wait_for_completion(&control->completion); > > > > > > Let's assume DAMON is terminated between the damon_is_running() and > > > list_add_tail(). In the case, the control->fn() will never be called back. If > > > control->repeat is false, this function will even inifnitely wait. > > > > As you said, there are cases where kdamond is terminated(stopped) in > > damon_is_running() and list_add_tail(). It may be a very rare case, but > > I missed this case. > > > > > > > > I think we should keep the damon_is_running() as is, but further check if it > > > was terminated without handling the control object, and remove it from the list > > > in the case. Like below. > [...] > > However, the damon_call_handle_inactive_ctx() function is to post-process > > the duplicate addition of control->list. Rather, it is more efficient to > > prevent duplicate additions in advance, as follows: > > I have tested the following and it works fine. > > > > @@ -1467,11 +1496,14 @@ int damon_call(struct damon_ctx *ctx, struct > > damon_call_control *control) > > control->canceled = false; > > INIT_LIST_HEAD(&control->list); > > > > - mutex_lock(&ctx->call_controls_lock); > > - list_add_tail(&control->list, &ctx->call_controls); > > - mutex_unlock(&ctx->call_controls_lock); > > - if (!damon_is_running(ctx)) > > + if (damon_is_running(ctx)) { > > + mutex_lock(&ctx->call_controls_lock); > > + list_add_tail(&control->list, &ctx->call_controls); > > + mutex_unlock(&ctx->call_controls_lock); > > + } else { > > + /* return damon_call_handle_inactive_ctx(ctx, control); */ > > return -EINVAL; > > + } > > if (control->repeat) > > return 0; > > wait_for_completion(&control->completion); > > I think this is not differnt from your previous suggestion, and thus it has the > same issue. What if DAMON is terminated between damon_is_running() and > list_add_tail() call? Please let me know if I'm missing something. I think it is good idea to insert a barrier() between damon_is_running() and list_add_tail() to prevent context-switching. What do you think this? Thanks, JaeJoon > > > > > > If you don't mind, I'll post the above diff as a patch, adding a 'Reported-by:' > > > tag for you. > > > > 'Reported-by:' is OK. However, please check the above again. > > Thank you! > > > Thanks, > SJ > > [...]