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Mon, 3 Nov 2025 04:08:28 +0000 (GMT) Message-ID: <01045c4c-a37a-4a31-8787-6483c7b78dad@linux.ibm.com> Date: Mon, 3 Nov 2025 09:38:27 +0530 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] crash: fix crashkernel resource shrink To: Baoquan He , Andrew Morton Cc: linux-kernel@vger.kernel.org, Zhen Lei , kexec@lists.infradead.org References: <20251101193741.289252-1-sourabhjain@linux.ibm.com> Content-Language: en-US From: Sourabh Jain In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-GUID: j7_qIb3WQBhRLN09Hp03kgr71H6BNM3d X-Proofpoint-ORIG-GUID: j7_qIb3WQBhRLN09Hp03kgr71H6BNM3d X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUxMTAxMDAyMSBTYWx0ZWRfX9LpHsbKoChLO 5+ONM7XtYP3EJBArimzGmzVbjHhjbuiK2WFslK6wr//QblruRZbLjqiHSI2Xjl05c8tJqts7Axq H2fmj/TH/llUhmHZQ/JTxSaf/lZIA5TiZS0SpCa8RQzaxyzDyMZxIub4MZT23fCERw+4EfFDpMj imng+Wel1VK/kL8S/w/DMFedCB3Yla8EI0N7VsKdz9usdqAApvD4CWbNMa9e0KKcm3bxdQ4Km9t OdsJgLhfQSjBkRaITl2QjZ/J6f3ZlC5TvPr2V3W/577+Cl8bKfJnghyb1Nod2KzKogXYlsvlvLl ao5leGC73uujqnTh7CDBI0anNCFAXK0ugRA95N96cDktBusv8RuhC00Dr5vr310FWy8eNHSkqTK IUbgqy9w3h+unEqe4hMiKXryKcr0fQ== X-Authority-Analysis: v=2.4 cv=H8HWAuYi c=1 sm=1 tr=0 ts=69082ac0 cx=c_pps a=bLidbwmWQ0KltjZqbj+ezA==:117 a=bLidbwmWQ0KltjZqbj+ezA==:17 a=IkcTkHD0fZMA:10 a=6UeiqGixMTsA:10 a=VkNPw1HP01LnGYTKEx00:22 a=Z4Rwk6OoAAAA:8 a=20KFwNOVAAAA:8 a=i0EeH86SAAAA:8 a=JfrnYn6hAAAA:8 a=VnNF1IyMAAAA:8 a=AF3erdo4s1WuFiYT4_sA:9 a=QEXdDO2ut3YA:10 a=HkZW87K1Qel5hWWM3VKY:22 a=1CNFftbPRP8L7MoqJWF3:22 a=cPQSjfK2_nFv0Q5t_7PE:22 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1121,Hydra:6.1.9,FMLib:17.12.100.49 definitions=2025-11-02_02,2025-10-29_03,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 phishscore=0 lowpriorityscore=0 priorityscore=1501 adultscore=0 impostorscore=0 clxscore=1015 bulkscore=0 suspectscore=0 malwarescore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.19.0-2510240000 definitions=main-2511010021 On 03/11/25 08:24, Baoquan He wrote: > On 11/02/25 at 01:07am, Sourabh Jain wrote: >> When crashkernel is configured with a high reservation, shrinking its >> value below the low crashkernel reservation causes two issues: >> >> 1. Invalid crashkernel resource objects >> 2. Kernel crash if crashkernel shrinking is done twice >> >> For example, with crashkernel=200M,high, the kernel reserves 200MB of >> high memory and some default low memory (say 256MB). The reservation >> appears as: >> >> cat /proc/iomem | grep -i crash >> af000000-beffffff : Crash kernel >> 433000000-43f7fffff : Crash kernel >> >> If crashkernel is then shrunk to 50MB (echo 52428800 > >> /sys/kernel/kexec_crash_size), /proc/iomem still shows 256MB reserved: >> af000000-beffffff : Crash kernel >> >> Instead, it should show 50MB: >> af000000-b21fffff : Crash kernel >> >> Further shrinking crashkernel to 40MB causes a kernel crash with the >> following trace (x86): >> >> BUG: kernel NULL pointer dereference, address: 0000000000000038 >> PGD 0 P4D 0 >> Oops: 0000 [#1] PREEMPT SMP NOPTI >> >> Call Trace: >> ? __die_body.cold+0x19/0x27 >> ? page_fault_oops+0x15a/0x2f0 >> ? search_module_extables+0x19/0x60 >> ? search_bpf_extables+0x5f/0x80 >> ? exc_page_fault+0x7e/0x180 >> ? asm_exc_page_fault+0x26/0x30 >> ? __release_resource+0xd/0xb0 >> release_resource+0x26/0x40 >> __crash_shrink_memory+0xe5/0x110 >> crash_shrink_memory+0x12a/0x190 >> kexec_crash_size_store+0x41/0x80 >> kernfs_fop_write_iter+0x141/0x1f0 >> vfs_write+0x294/0x460 >> ksys_write+0x6d/0xf0 >> >> >> This happens because __crash_shrink_memory()/kernel/crash_core.c >> incorrectly updates the crashk_res resource object even when >> crashk_low_res should be updated. >> >> Fix this by ensuring the correct crashkernel resource object is updated >> when shrinking crashkernel memory. >> >> Fixes: 16c6006af4d4 ("kexec: enable kexec_crash_size to support two crash kernel regions") >> Cc: Andrew Morton >> Cc: Baoquan He >> Cc: Zhen Lei >> Cc: kexec@lists.infradead.org >> Signed-off-by: Sourabh Jain >> --- >> kernel/crash_core.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/kernel/crash_core.c b/kernel/crash_core.c >> index 3b1c43382eec..99dac1aa972a 100644 >> --- a/kernel/crash_core.c >> +++ b/kernel/crash_core.c >> @@ -373,7 +373,7 @@ static int __crash_shrink_memory(struct resource *old_res, >> old_res->start = 0; >> old_res->end = 0; >> } else { >> - crashk_res.end = ram_res->start - 1; >> + old_res->end = ram_res->start - 1; > It's a code bug, nice catch, thanks. > > Acked-by: Baoquan He Thanks for the ack, Baoquan. - Sourabh Jain