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Wed, 22 Jul 2026 08:35:26 +0000 (GMT) Received: from [9.224.77.173] (unknown [9.224.77.173]) by smtpav05.fra02v.mail.ibm.com (Postfix) with ESMTP; Wed, 22 Jul 2026 08:35:25 +0000 (GMT) Message-ID: <83290932-cb8b-4741-bff0-6a7d8df2c637@linux.ibm.com> Date: Wed, 22 Jul 2026 10:35:25 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH/RFC] btrfs: fix folio lock leak in writepage_delalloc() for folios dirtied behind btrfs' back To: Qu Wenruo , linux-btrfs@vger.kernel.org, Qu Wenruo Cc: David Sterba , Chris Mason , Josef Bacik , linux-kernel@vger.kernel.org, kvm@vger.kernel.org, linux-s390@vger.kernel.org References: <20260721191152.101118-1-borntraeger@linux.ibm.com> <20260721191152.101118-2-borntraeger@linux.ibm.com> Content-Language: en-US From: Christian Borntraeger In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-Reinject: loops=2 maxloops=12 X-Proofpoint-ORIG-GUID: _mzbYkPGzxBvwZIsNGHvhmFwqjqYiEVA X-Authority-Analysis: v=2.4 cv=V6RNF+ni c=1 sm=1 tr=0 ts=6a6080d2 cx=c_pps a=GFwsV6G8L6GxiO2Y/PsHdQ==:117 a=GFwsV6G8L6GxiO2Y/PsHdQ==:17 a=IkcTkHD0fZMA:10 a=RAioF0-LDSMA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=U7nrCbtTmkRpXpFmAIza:22 a=lEjgxdKC6ZHkbqwYjkIA:9 a=3ZKOabzyN94A:10 a=QEXdDO2ut3YA:10 X-Proofpoint-Spam-Info: AW1haW4tMjYwNzIyMDA3NiBTYWx0ZWRfXyGLPGDP2vbEj xMfWmDcg0apWLLCqd2cKsB/9I7bHctn0osX38LoGmsk8i3zhVp+fQThg0mu+mi1JuFitXkJ+ELd u6avby2E6Y/dRH4bMJCwxZ8PuXgdnks= X-Proofpoint-GUID: xJaR1kY_-9f5HcRkVD3uL3fjtbNscKvv X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNzIyMDA3NiBTYWx0ZWRfX4n4DDF+G5WJ6 Y6wRBS0BREuAManMEekI/fbKLEnkBaTl9fwtCQM3S0gI7fGOdDpmve/8AaX/TjJAdtjSEyRTESk LKfm/+FrH4RRJdDgRUAfbqnXKuSs9cava7MvMw8Ik8D6Sju69cuyyHeLGr/sTxEm28lLDrySt9r jllt6m5tfpbFtGjVDv9hc+KrbqAqQhR0ZKPCIGah+tIb7aOqkpOt/oMj15t6X1wiIzBpC4s9yeE qACK3PNE1I7ymm1jZoOF5J6yRKCbqSZRzq9H6ZsBoN/i7O5HOky1BDMeBxi3xcdRdg5Pl2VY1W4 g3URAxscIu32FstgqtcFu067m5GA44GYNUOxztGwf6k8C4XqQEf0mzY7XdbUYW7ALEkKHh8VCXV rp/M/uO1WaOy4ovq15BTh0YEHHhUBypq08nFyenAfjsZ3Xsitwwt4k81u5ppEorwRZNVJ0EdtNr M/lqrGY1wws5tF6sPJw== X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1143,Hydra:6.1.134,FMLib:17.12.100.49 definitions=2026-07-22_02,2026-07-21_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 malwarescore=0 adultscore=0 bulkscore=0 lowpriorityscore=0 clxscore=1015 spamscore=0 impostorscore=0 phishscore=0 priorityscore=1501 suspectscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2607220076 Am 21.07.26 um 23:07 schrieb Qu Wenruo: First, thank you for taking the time to look into this and trying to understand things and trying to explain things. this is highly appreciated. I am still trying to fully understand this myself. A question: > 在 2026/7/22 04:41, Christian Borntraeger 写道: >> A folio can carry the folio-level dirty flag while its btrfs subpage >> dirty bitmap is empty: btrfs data mappings use filemap_dirty_folio(), >> so a generic folio_mark_dirty() call sets only the folio flag and the >> xarray tag, without setting any subpage dirty bit and without a >> delalloc reservation.  The typical source is set_page_dirty_lock() on >> a GUP pin, > > Shouldn't such folio got its ->page_mkwrite() callback get called first? Isnt that called implicitely at pin time? At unpin, set_page_dirty_lock() re-dirties the now-clean folio. From what I can see, this is not an s390 invention but a sanctioned pattern. But I can certainly not exclude that this is still an s390 specific problem. Let me dig a bit deeper. Thanks again for your quick response. Christian