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b=oTlKDKdUnmgfyYNkASSEovavhFg0JzcPEcID2tWKD+t9hZfDJIphX6Jwe4Ovvb0fw NakPVIK08JsWL08u9dQpaD2h5EcPIXxFn0vg+3fn9u/KKKtVvfEN+pe/Rrq87fDPYX izLXK/AkoxyMwP2PMH43/WVP3p1Cr6bqwLSYlxBu61OjSvcp8Rm1zRrhKkuAuZHOtO z3ywTtyCOBYy1/NIHPxQPgmqND/5wuLB2r3+tjf1FCmvvFci7ijoxyA/Rl0C7TRxE4 WsBAoVoWZSkq/Xrb6PU+i54mTsoMi+J2aTPXrDdHRX3G1OXCtKA+xi2kHObVpz3hCl ERRYYI8whqoBg== From: SeongJae Park To: SeongJae Park Cc: Andrew Morton , damon@lists.linux.dev, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [RFC PATCH 02/10] mm/damon/sysfs: add pause file under context dir Date: Mon, 16 Mar 2026 21:26:36 -0700 Message-ID: <20260317042637.917-1-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260315210012.94846-3-sj@kernel.org> References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Stat-Signature: 8cq1ac7n894cdigdmb4szpuxrmj96xpn X-Rspamd-Server: rspam09 X-Rspam-User: X-Rspamd-Queue-Id: 9B3D920002 X-HE-Tag: 1773721605-581907 X-HE-Meta: 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 DlhMG/9/ tbsb2U8gmHYLchKr2IOkjbm72MzwtKlNVVbVhh8IVB3spn9JQhCLuzDm1wC5KTv6hhI3AMYu7E3nT1lMTrK4EVoWAM8Dj91d/rEHBoBWdQWhM76J+Vc7Tdp5nt5mEmkHWf9d3uptRmFxMCoUCD8zCBJd+4EzK+8udCeOZKMIDN2XRTmqfgJcX2gmDirOaizmgTme+ONk2PC62pNc29k5I8MUW9IFey5QxC1nrKg7jeeynxZ/fo06u21x9Mwu5KMMFw25vJMWmQplrvQGcEllRkLi3UTsSpkXFQY6k Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Sun, 15 Mar 2026 14:00:01 -0700 SeongJae Park wrote: > Add pause DAMON sysfs file under the context directory. It exposes the > damon_ctx->pause API parameter to the users so that they can use the > pause/resume feature. > > Signed-off-by: SeongJae Park > --- > mm/damon/sysfs.c | 30 ++++++++++++++++++++++++++++++ > 1 file changed, 30 insertions(+) > > diff --git a/mm/damon/sysfs.c b/mm/damon/sysfs.c > index 576d1ddd736bf..4cbb8b9aaba3c 100644 > --- a/mm/damon/sysfs.c > +++ b/mm/damon/sysfs.c > @@ -866,6 +866,7 @@ struct damon_sysfs_context { > struct damon_sysfs_attrs *attrs; > struct damon_sysfs_targets *targets; > struct damon_sysfs_schemes *schemes; > + bool pause; > }; sashiko.dev comments [1] below. : Is the new pause field left uninitialized when a context is allocated? : : Looking at damon_sysfs_context_alloc(), memory is allocated via kmalloc_obj() : which does not zero-fill by default, and the new field is not explicitly : initialized: : : static struct damon_sysfs_context *damon_sysfs_context_alloc( : enum damon_ops_id ops_id) : { : struct damon_sysfs_context *context = kmalloc_obj(*context); : : if (!context) : return NULL; : context->kobj = (struct kobject){}; : context->ops_id = ops_id; : context->addr_unit = 1; : return context; : } : : If a user reads the pause sysfs file before writing to it, could this return : uninitialized kernel heap memory? Good catch. I will add below fixup to the next spin. ''' --- a/mm/damon/sysfs.c +++ b/mm/damon/sysfs.c @@ -1432,6 +1432,7 @@ static struct damon_sysfs_context *damon_sysfs_context_alloc( context->kobj = (struct kobject){}; context->ops_id = ops_id; context->addr_unit = 1; + context->pause = false; return context; } ''' Btw, somehow sashiko.dev added the comment to not this patch but the sixth patch of this series. [1] https://sashiko.dev/#/patchset/20260315210012.94846-7-sj@kernel.org Thanks, SJ [...]