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b=Xvw5F5tP1fw4iN14lQQ2Nt3VdLPMhT6KyQZLrvk3kESsKR2+6uixcAKkA6gINcgVA stW1h0g6/KM//E0BZS8FyBKPSpsOhmL7ztuNbB4G3wl5MZWDyXh3NDQbIHEuzvHK3p Lfr/M8R4dLbBs9y1InjELI/TgB1QoNoqlOdbK92C1zTRdWV1V0cSmYVCrovjmF0c9x F6byvPURDYE1PwpUspAynEkzjhRZIc+bmolhvmolE0Mcw4juHtc74ff31w1jDxVQNp B47r+5ecFAVTyAlDX51q1d4gDa2zP08Mby8Dv1UeYjnGPJvGswHS55yX40YD0WsCZi kYoZ9QpDp2euA== From: SeongJae Park To: SeongJae Park Cc: "# 6 . 17 . x" , Andrew Morton , damon@lists.linux.dev, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: (sashiko review) [RFC PATCH] mm/damon/stat: deallocate damon_call() failure leaking damon_ctx Date: Thu, 2 Apr 2026 08:27:15 -0700 Message-ID: <20260402152716.75168-1-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260402133952.73301-1-sj@kernel.org> References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: ADC70100005 X-Stat-Signature: yzmzxscojws6x6yq9hthnj7ftkof6y78 X-Rspam-User: X-Rspamd-Server: rspam02 X-HE-Tag: 1775143638-555874 X-HE-Meta: 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 CPBi1HGX CWX/mVYVreHHFdAT8/NKpgAc6B7WjvZu0fTI2GAPW2XsUSN0Rcm1eA68bDnKW6qBliS9yod4o4ljuvfzN2osWYjBad1Pz9Ory6/zDPaIyglNQiRsaf9ZiCRPHSfPU9rIDzGTxl0IkEZBdeIiVsYyknmwyBpy3rt5q/tMmL8Hq81QHqL/V/h57zfDC4o87nzoL/WMDCa/9QzzG9uapPHDh/vzg31k6GpwqAI9imQK56EyIFbdMzLOztwzkRaJFe4VC5kqFgytviaZRRE6GVk2OWQE3q5/hYF4p26Tz/5MBWt4uuELDH3mwdvonSNExj8DRgYSkig8AbzXQveE= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, 2 Apr 2026 06:39:51 -0700 SeongJae Park wrote: > TL; DR: sashiko didn't find a real issue here. I will post non-RFC patch soon. Posted it: https://lore.kernel.org/20260402134418.74121-1-sj@kernel.org [...] > > Forwarding Sashiko review in a usual reply format, with my inline comment for > doing discussions via mails. > > > # review url: https://sashiko.dev/#/patchset/20260402045928.71170-1-sj@kernel.org > > # start of sashiko.dev inline review > > commit 8adb3c95d68d8448c8f57865d9874a5277cc1540 > > Author: SeongJae Park > > > > mm/damon/stat: deallocate damon_call() failure leaking damon_ctx > > > > This commit attempts to fix a memory leak of the damon_ctx object when > > damon_call() fails, by deferring deallocation to a subsequent start call > > to avoid a use-after-free with the terminating kdamond thread. > > > > Link: https://lore.kernel.org/20260401012428.86694-1-sj@kernel.org > > > > > diff --git a/mm/damon/stat.c b/mm/damon/stat.c > > > --- a/mm/damon/stat.c > > > +++ b/mm/damon/stat.c > > > @@ -245,6 +245,12 @@ static int damon_stat_start(void) > > > { > > > int err; > > > > > > + if (damon_stat_context) { > > > + if (damon_is_running(damon_stat_context)) > > > + return -EAGAIN; > > > > If the user retries while the background thread is still terminating, this > > will return -EAGAIN. Does this break standard sysfs boolean expectations, > > forcing userspace scripts to implement arbitrary retry loops? > > I don't think that's a problem. > > > > > Also, if the user never writes "Y" to the "enabled" sysfs parameter again, > > does the memory remain permanently leaked? > > In a sense someone can argue so. Someone else may also argue it as "cached". > Anyway the total amount of "leaked" or "cached" memory is just single damon_ctx > object. No problem in my opinion. Because the reference is still there, I think it cannot technically be called "leaked". Thanks, SJ [...]