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b=e+/9ST3PGkPi1y5hG0RIrAS/NuJn6hslhp3Gipi/d9GijnRwr2umKOd8vR8sHoAmz O7lUlcHrso/j4ZRWPjacyR/UOTGBjKqnpjkMF2FXF/yBsvNmDzLBH6uoSNthDMK2Sl jfoIbroFu8FIx4yh5ZoyzsG/CQExbhl8lynXDfYvu98Yjvy6ZDJZ50VWdxO8Vu7rmc D36WHitrvXq7Bb7Nw4/TEp4De02IWlJ+1LjzOie5vWv4L/dC9ZPQ9ucn3EkQQLbztY 2+SKiyOrW0r9ugf0EdULJTTU3F8XIJEXOdiz3LB2Hzua7iDs8bYbTUtCp9jNvfDIjX Vmsbly21Hloqg== From: SeongJae Park To: SeongJae Park Cc: Andrew Morton , "# 6 . 15 . x" , damon@lists.linux.dev, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH] mm/damon/core: avoid use of half-online-committed context Date: Fri, 20 Mar 2026 19:25:10 -0700 Message-ID: <20260321022510.79038-1-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260321021628.78887-1-sj@kernel.org> References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 46235180003 X-Stat-Signature: 987to1qw9t4kq3g4o6tkabubhzm93hm9 X-Rspam-User: X-HE-Tag: 1774059919-944971 X-HE-Meta: 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 l7n9Myd9 c2q3z8vE/AlRNlrbLpwWtTLzZOA7FHfqjYkZ4pDtzqxy6t2XLUaujcaxnKSo88v2RnH+MY4Ufa3ASU1xgGmiSCzntnhw/3QFEckPjMTokZkpcUUgl5yBoXOa3VfugUwQBHIK1fmDu6len1I5dkwrXLq8AS+DE6lv+07cD+w85x66NWShJm06v53q9rSpjz2ugwyFNhsv0eq57RH4BL3d7HU0WMmsypzE1ZgO76MUFMgdqAiTSl2hcEbjEDv6iGLfPfbSxWE0ggnPhQSSKukudTRJMmVtv2xKpyRjDKlOBRzf/WyduODlaRLiXUvOV3wmg0TOtsa/mAHXqEp7eEi2+zsJ0fHsRQP8sKjJTY4quo4lCofIcBywUePeuZT1Xs6KyfcSAIVSZcrvCDwI= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, 20 Mar 2026 19:16:27 -0700 SeongJae Park wrote: > On Thu, 19 Mar 2026 19:48:49 -0700 Andrew Morton wrote: > > > On Thu, 19 Mar 2026 07:52:17 -0700 SeongJae Park wrote: > > > > > One major usage of damon_call() is online DAMON parameters update. It > > > is done by calling damon_commit_ctx() inside the damon_call() callback > > > function. damon_commit_ctx() can fail for two reasons: 1) invalid > > > parameters and 2) internal memory allocation failures. In case of > > > failures, the damon_ctx that attempted to be updated (commit > > > destination) can be partially updated (or, corrupted from a > > > perspective), and therefore shouldn't be used anymore. The function > > > only ensures the damon_ctx object can safely deallocated using > > > damon_destroy_ctx(). > > > > > > The API callers are, however, calling damon_commit_ctx() only after > > > asserting the parameters are valid, to avoid damon_commit_ctx() fails > > > due to invalid input parameters. But it can still theoretically fail if > > > the internal memory allocation fails. In the case, DAMON may run with > > > the partially updated damon_ctx. This can result in unexpected > > > behaviors including even NULL pointer dereference in case of > > > damos_commit_dests() failure [1]. Such allocation failure is arguably > > > too small to fail, so the real world impact would be rare. But, given > > > the bad consequence, this needs to be fixed. > > > > > > Avoid such partially-committed (maybe-corrupted) damon_ctx use by saving > > > the damon_commit_ctx() failure on the damon_ctx object. For this, > > > introduce damon_ctx->maybe_corrupted field. damon_commit_ctx() sets it > > > when it is failed. kdamond_call() checks if the field is set after each > > > damon_call_control->fn() is executed. If it is set, ignore remaining > > > callback requests and return. All kdamond_call() callers including > > > kdamond_fn() also check the maybe_corrupted field right after > > > kdamond_call() invocations. If the field is set, break the > > > kdamond_fn() main loop so that DAMON sill doesn't use the context that > > > might be corrupted. > > > > I guess you saw the AI review? > > https://sashiko.dev/#/patchset/20260319145218.86197-1-sj%40kernel.org > > By the way, I am also doing monitoring of sashiko.dev for all DAMON patches. > It will be much easier once sashiko.dev's email feature is ready, since I > already onboarded DAMON for that. > > Meanwhile, the monitoring using web browser is somewhat tedious for me, so I > just implemented an hkml feature, namely > 'hkml patch sashiko_dev --thread_status'. It receives a message id of a mail, > and prints the review status/result of all patches of the thread. > > E.g., > > $ hkml patch sashiko_dev --thread_status 20260319-memory-failure-mf-delayed-fix-rfc-v2-v2-0-92c596402a7a@google.com > - [PATCH RFC v2 1/7] mm: memory_failure: Clarify the MF_DELAYED definition > - Reviewed (Review completed successfully.) > - [PATCH RFC v2 2/7] mm: memory_failure: Allow truncate_error_folio to return MF_DELAYED > - Reviewed (Review completed successfully.) > - [PATCH RFC v2 3/7] mm: shmem: Update shmem handler to the MF_DELAYED definition > - Reviewed (Review completed successfully.) > - [PATCH RFC v2 4/7] mm: memory_failure: Generalize extra_pins handling to all MF_DELAYED cases > - Pending (None) > - [PATCH RFC v2 4/7] mm: memory_failure: Generalize extra_pins handling to all MF_DELAYED cases > - Reviewed (Review completed successfully.) > - [PATCH RFC v2 5/7] mm: selftests: Add shmem memory failure test > - Reviewed (Review completed successfully.) > - [PATCH RFC v2 6/7] KVM: selftests: Add memory failure tests in guest_memfd_test > - Reviewed (Review completed successfully.) > - [PATCH RFC v2 7/7] KVM: selftests: Test guest_memfd behavior with respect to stage 2 page tables > - Reviewed (Review completed successfully.) > > I'm planning to implement another feature for formatting and sending the review > result and inline comments as emails, probably this weekend. I wanted to add the link to the commit that implementing the feature, but forgot that, sorry. Here it is: https://github.com/sjp38/hackermail/commit/cf1b4e167067e5684823137c5296dfb268364175 FWIW, iiuc, 'b4 review' should also provide similar or better feature. Thanks, SJ [...]