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Wed, 12 Aug 2026 07:53:36 +0000 (GMT) Received: from tuxmaker.boeblingen.de.ibm.com (unknown [9.87.85.9]) by smtpav07.fra02v.mail.ibm.com (Postfix) with ESMTP; Wed, 12 Aug 2026 07:53:36 +0000 (GMT) From: Peter Oberparleiter To: Heiko Carstens , Vasily Gorbik , Alexander Gordeev Cc: linux-s390@vger.kernel.org, Ilya Leoshkevich , Peter Oberparleiter Subject: [PATCH] s390/debug: Fix deadlock during unregister Date: Wed, 12 Aug 2026 09:53:19 +0200 Message-ID: <20260812075319.2007940-1-oberpar@linux.ibm.com> X-Mailer: git-send-email 2.53.0 Precedence: bulk X-Mailing-List: linux-s390@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Authority-Analysis: v=2.4 cv=AMtp2X5w c=1 sm=1 tr=0 ts=6a7c2684 cx=c_pps a=GFwsV6G8L6GxiO2Y/PsHdQ==:117 a=GFwsV6G8L6GxiO2Y/PsHdQ==:17 a=Sv0fKeRqtYgA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=Y2IxJ9c9Rs8Kov3niI8_:22 a=VnNF1IyMAAAA:8 a=6BefsEoFRu_C_CthcTgA:9 X-Proofpoint-GUID: VNTYeSSMdVi-HDijB0-mphaXFwJ5Bkhw X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwODEyMDA1OSBTYWx0ZWRfX2Jtax1V2YdJR 1lrpUQGAVqKNoRGFPzCo2Ngo8uIUrwTobseTug3xzA9KNn+/DvjFsiGvO4H+hlo8Fy12Eqjl9op OQM/WXMOyiZPq+GZ+/QjUh53YboOddIiYfZY+UKSWL8qOjZJfVfEWPtAYEZ2JouDbm/EBzJDsHn ZW2wUMckln6iDvsrjoLbgJSIOXiFMPy886DKMyAd0ktq3LL8vedZvonEcKt8WR066/1+cABSpvp Kh5hMzc7OprJwEFzDigHJUnCc6hRGauqEf7rnW7/mY4gSYf5x131DzWTkIxrueDfivu901ommja VtHdRSgQRsc6+nph5kB4MHawlet2H8Xc907DVeN2bUA7zky/SAsxNiZ+HQ6zN4nTMj1UwslAUGM o3ZzECSmukSMLTYdsH+Ycg/BysFYt4l1f65SDT9rd3+K6q47E10ezJkqKNEj4rGK/6OhbD3pbym ftVgYPiR5SdNyf5zmbA== X-Proofpoint-ORIG-GUID: VNTYeSSMdVi-HDijB0-mphaXFwJ5Bkhw X-Proofpoint-Spam-Info: AW1haW4tMjYwODEyMDA1OSBTYWx0ZWRfX5zZzoTPyRul6 Luv2DFOBm/Co2dNp0p5P8L+7vxDfpctekNm0Xbtroiu63th/fNbfJQV/iLeBUNZJXivVWeiR+X6 ufU8YPzEl0JcaCl/XQFsSBVvmehVM0g= X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1176,Hydra:6.1.134,FMLib:17.12.100.49 definitions=2026-08-12_02,2026-08-10_03,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 suspectscore=0 adultscore=0 lowpriorityscore=0 clxscore=1015 priorityscore=1501 impostorscore=0 phishscore=0 spamscore=0 bulkscore=0 malwarescore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2608120059 Unregistering an s390dbf debug area while one of the associated debugfs files is being written to can cause a deadlock: $ echo >.../vmur/level $ rmmod vmur =================================================== debugfs write debugfs_file_get() debug_unregister() mutex_lock(debug_mutex) debugfs_remove() wait for debugfs_file_put() debug_file_ops.write() debug_input() mutex_lock(debug_mutex) ==> DEADLOCK Fix this by splitting debug_unregister() into an s390dbf and debugfs part, and running only the s390dbf part with debug_mutex locked. Signed-off-by: Peter Oberparleiter --- arch/s390/kernel/debug.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-) diff --git a/arch/s390/kernel/debug.c b/arch/s390/kernel/debug.c index dbf430f479bd..14d2b58ad093 100644 --- a/arch/s390/kernel/debug.c +++ b/arch/s390/kernel/debug.c @@ -993,8 +993,8 @@ void debug_register_static(debug_info_t *id, int pages_per_area, int nr_areas) mutex_unlock(&debug_mutex); } -/* Remove debugfs entries and remove from internal list. */ -static void _debug_unregister(debug_info_t *id) +/* Remove debugfs entries. */ +static void _debug_unregister_debugfs(debug_info_t *id) { int i; @@ -1004,6 +1004,11 @@ static void _debug_unregister(debug_info_t *id) debugfs_remove(id->debugfs_entries[i]); } debugfs_remove(id->debugfs_root_entry); +} + +/* Remove from internal list. */ +static void _debug_unregister(debug_info_t *id) +{ if (id == debug_area_first) debug_area_first = id->next; if (id == debug_area_last) @@ -1029,6 +1034,7 @@ void debug_unregister(debug_info_t *id) mutex_lock(&debug_mutex); _debug_unregister(id); mutex_unlock(&debug_mutex); + _debug_unregister_debugfs(id); debug_info_put(id); } -- 2.53.0