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b=mxBE6pmUjzBw8X/vSAoaJgCPYiZsiY77HLBcz2e5ZMAnr5PMmO14Kb26I8ltmiFXI m/5vtkkMyHe40rMQil8dcWgyZd36DinyeXcQBOTLG0IIwaMlxnkjP+jl0c0augEF7p vPa2navhz8nyfwi0F+tVv3SPzSdRwFJa4xNzfznc0AK7Biow3gcUWqB1Dyr/q6DrAA I8aqDkvAh6qy0Tdddqj9vv++PSsjvSuwN6aEgG5hyTSNH+vE2jwUAWJ8qhli9cvpEr UJQg5uluHHcN5qtwdb024EQYO0IZ9wFCEcLWqgGhBEAVGfujIPgd92mMySLKRETW96 1qOzRTkwV2rGg== From: SeongJae Park To: Andrew Morton Cc: SeongJae Park , "# 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 19:16:27 -0700 Message-ID: <20260321021628.78887-1-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260319194849.64b0911e2a7a6d8b1c22005a@linux-foundation.org> References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 58EF4C0004 X-Stat-Signature: d8aomica3yfm1r641p3fzbfp3a3gitkr X-Rspam-User: X-HE-Tag: 1774059396-45653 X-HE-Meta: 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 ONhPJgFM 5X5j0C2DhDku0T5eeQMVwDdPaDqxQ8rGcR5hLAig/h1F2+HxVVYgjKjvp/BLx4Qw+rSoDcg2SEbAhnpfVdvPNR/1toCu0dnjLLuwM3F9dnmFO/H1clogaQSqWYI3JbNUICzLHoVOMDf5f0eGBt7W4TLY0pkVIOpMDx5U3Yf4oOAlmHlzSFAKy4SbSDxFNORk5tBOyVzWiZwe0voRJprFFbSMAfOc9pfbzcBWwUFPlQY5dwBCwber1NPTuJpj6OC6nJj8m5cahem/t19M/+lTssCvbVCRW6hci9uPG5lY3dvG8KgHyNWYB9HBPxR+KWNmzuBbA5EcMczjh1dy9NGrh1b/eisYNpt7o/3K2ByZ02S3Ltuy3DsmbRslOdA== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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. Thanks, SJ