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Thu, 29 Oct 2026 19:57:13 -0700 (PDT) Received: from localhost ([27.122.242.71]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-8a9eef95cb5sm162643b3a.9.2026.10.29.19.57.12 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 29 Oct 2026 19:57:12 -0700 (PDT) Date: Fri, 30 Oct 2026 11:57:10 +0900 From: Hyunchul Lee To: Shengzhuo Wei Cc: liubaolin , Namjae Jeon , ntfs@lists.linux.dev, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH] ntfs: wait for bitmap folio writeback before modifying it Message-ID: References: <20261029-b4-ntfs-bitmap-writeback-wait-v1-1-e2ba711b2dbf@cherr.cc> <374bf856-f880-4fa2-abec-c4b2a063bf57@163.com> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Hi Shengzhuo, On Thu, Oct 29, 2026 at 02:17:56PM +0800, Shengzhuo Wei wrote: > On 2026-10-29 10:07, liubaolin wrote: > > > Hi Shengzhuo, > > Could this deadlock during MFT bitmap > > expansion？ntfs_mft_bitmap_extend_allocation_nolock() can recurse into MFT > > record allocation while holding mftbmp_ni->runlist.lock. > > > > With L being that lock, could we get the following interleaving? > > A and B are $MFT::$BITMAP folios; B is outside the cached iomap. > > Time flows downwards. > > > > Writeback Bitmap expansion > > --------- ---------------- > > lock A > > set PG_writeback(A) > > map A (take/release L) > > add A to wpc->wb_ctx > > unlock A > > [BIO still unsubmitted] > > take L > > extend bitmap mapping pairs > > need another extent record > > ntfs_mft_record_alloc() > > mft_bitmap_alloc_free_rec() > > lock A > > folio_wait_writeback(A) > > [wait for A's I/O, holding L] > > > > lock B > > set PG_writeback(B) > > ntfs_writeback_range(B) > > __ntfs_write_iomap_begin() > > down_write(L) > > [blocked on L] > > > > Cannot reach iomap_add_to_ioend() > > to submit A's pending BIO. Cannot release L until > > A's writeback completes. > > > > ntfs_writeback_range() obtains the next mapping before > > iomap_add_to_ioend() can submit the pending BIO. > > Would we need to submit that BIO before taking the mapping locks? > > > > Thanks, > > Baolin. > > > > Hi Baolin, > > Thanks for the analysis. I checked the paths and agree with you. > > Following your suggestion, I prepared a change to submit the pending > ioend before obtaining a new mapping in ntfs_writeback_range(), clearing > wpc->wb_ctx even on error to avoid resubmission. I plan to make this a > prerequisite for v2, retaining all six waits. > > One concern is that submitting at mapping boundaries may reduce BIO > aggregation, including for ordinary file writeback. The change has > passed object builds, but has not been runtime- or performance-tested. > > Does this approach look reasonable to you? I think the early submit should be limited to $MFT:$BITMAP only. > > Thanks, > Shengzhuo -- Thanks, Hyunchul