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Wed, 13 May 2026 07:50:34 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id /fpZCUotBGrkBwAAD6G6ig (envelope-from ); Wed, 13 May 2026 07:50:34 +0000 Message-ID: Date: Wed, 13 May 2026 09:50:33 +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: BUG: drm/ast: soft lockup due to missing timeout in hardware polling (ast_2500_patch_ahb) To: w15303746062@163.com, Dave Airlie , Jocelyn Falempe Cc: Maarten Lankhorst , Maxime Ripard , David Airlie , Simona Vetter , dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, Mingyu Wang <25181214217@stu.xidian.edu.cn> References: <20260513073649.352831-1-w15303746062@163.com> Content-Language: en-US From: Thomas Zimmermann Autocrypt: addr=tzimmermann@suse.de; keydata= xsBNBFs50uABCADEHPidWt974CaxBVbrIBwqcq/WURinJ3+2WlIrKWspiP83vfZKaXhFYsdg XH47fDVbPPj+d6tQrw5lPQCyqjwrCPYnq3WlIBnGPJ4/jreTL6V+qfKRDlGLWFjZcsrPJGE0 BeB5BbqP5erN1qylK9i3gPoQjXGhpBpQYwRrEyQyjuvk+Ev0K1Jc5tVDeJAuau3TGNgah4Yc hdHm3bkPjz9EErV85RwvImQ1dptvx6s7xzwXTgGAsaYZsL8WCwDaTuqFa1d1jjlaxg6+tZsB 9GluwvIhSezPgnEmimZDkGnZRRSFiGP8yjqTjjWuf0bSj5rUnTGiyLyRZRNGcXmu6hjlABEB AAHNJ1Rob21hcyBaaW1tZXJtYW5uIDx0emltbWVybWFubkBzdXNlLmRlPsLAjgQTAQgAOAIb AwULCQgHAgYVCgkICwIEFgIDAQIeAQIXgBYhBHIX+6yM6c9jRKFo5WgNwR1TC3ojBQJftODH AAoJEGgNwR1TC3ojx1wH/0hKGWugiqDgLNXLRD/4TfHBEKmxIrmfu9Z5t7vwUKfwhFL6hqvo lXPJJKQpQ2z8+X2vZm/slsLn7J1yjrOsoJhKABDi+3QWWSGkaGwRJAdPVVyJMfJRNNNIKwVb U6B1BkX2XDKDGffF4TxlOpSQzdtNI/9gleOoUA8+jy8knnDYzjBNOZqLG2FuTdicBXblz0Mf vg41gd9kCwYXDnD91rJU8tzylXv03E75NCaTxTM+FBXPmsAVYQ4GYhhgFt8S2UWMoaaABLDe 7l5FdnLdDEcbmd8uLU2CaG4W2cLrUaI4jz2XbkcPQkqTQ3EB67hYkjiEE6Zy3ggOitiQGcqp j//OwE0EWznS4AEIAMYmP4M/V+T5RY5at/g7rUdNsLhWv1APYrh9RQefODYHrNRHUE9eosYb T6XMryR9hT8XlGOYRwKWwiQBoWSDiTMo/Xi29jUnn4BXfI2px2DTXwc22LKtLAgTRjP+qbU6 3Y0xnQN29UGDbYgyyK51DW3H0If2a3JNsheAAK+Xc9baj0LGIc8T9uiEWHBnCH+RdhgATnWW GKdDegUR5BkDfDg5O/FISymJBHx2Dyoklv5g4BzkgqTqwmaYzsl8UxZKvbaxq0zbehDda8lv hFXodNFMAgTLJlLuDYOGLK2AwbrS3Sp0AEbkpdJBb44qVlGm5bApZouHeJ/+n+7r12+lqdsA EQEAAcLAdgQYAQgAIAIbDBYhBHIX+6yM6c9jRKFo5WgNwR1TC3ojBQJftOH6AAoJEGgNwR1T C3ojVSkIALpAPkIJPQoURPb1VWjh34l0HlglmYHvZszJWTXYwavHR8+k6Baa6H7ufXNQtThR yIxJrQLW6rV5lm7TjhffEhxVCn37+cg0zZ3j7zIsSS0rx/aMwi6VhFJA5hfn3T0TtrijKP4A SAQO9xD1Zk9/61JWk8OysuIh7MXkl0fxbRKWE93XeQBhIJHQfnc+YBLprdnxR446Sh8Wn/2D Ya8cavuWf2zrB6cZurs048xe0UbSW5AOSo4V9M0jzYI4nZqTmPxYyXbm30Kvmz0rYVRaitYJ 4kyYYMhuULvrJDMjZRvaNe52tkKAvMevcGdt38H4KSVXAylqyQOW5zvPc4/sq9c= In-Reply-To: <20260513073649.352831-1-w15303746062@163.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Spam-Flag: NO X-Spam-Score: -0.80 X-Spamd-Result: default: False [-0.80 / 50.00]; SEM_URIBL(3.50)[xidian.edu.cn:email]; BAYES_HAM(-3.00)[100.00%]; NEURAL_HAM_LONG(-1.00)[-1.000]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; URIBL_BLOCKED(0.00)[suse.com:url,imap1.dmz-prg2.suse.org:helo,suse.de:mid,xidian.edu.cn:email]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; FREEMAIL_TO(0.00)[163.com,redhat.com]; FUZZY_RATELIMITED(0.00)[rspamd.com]; TO_MATCH_ENVRCPT_ALL(0.00)[]; MIME_TRACE(0.00)[0:+]; ARC_NA(0.00)[]; FREEMAIL_ENVRCPT(0.00)[163.com,gmail.com]; RCVD_TLS_ALL(0.00)[]; TO_DN_SOME(0.00)[]; FROM_EQ_ENVFROM(0.00)[]; FROM_HAS_DN(0.00)[]; FREEMAIL_CC(0.00)[linux.intel.com,kernel.org,gmail.com,ffwll.ch,lists.freedesktop.org,vger.kernel.org,stu.xidian.edu.cn]; RCVD_COUNT_TWO(0.00)[2]; RCPT_COUNT_SEVEN(0.00)[10]; MID_RHS_MATCH_FROM(0.00)[]; RCVD_VIA_SMTP_AUTH(0.00)[]; DBL_BLOCKED_OPENRESOLVER(0.00)[xidian.edu.cn:email,imap1.dmz-prg2.suse.org:helo,suse.com:url,suse.de:mid] X-Spam-Level: Hi Am 13.05.26 um 09:36 schrieb w15303746062@163.com: > From: Mingyu Wang <25181214217@stu.xidian.edu.cn> > > Hi all, > > While analyzing the AST driver's hardware interactions using our custom device emulation and fuzzing framework (DevGen), we observed a severe soft lockup in the DRM driver. > > Although the underlying trigger in our environment was an incomplete emulation of the ASPEED AHB bridge, this highlighted a critical defensive programming gap in the driver itself: a complete lack of timeout mechanisms in the hardware polling loops. > > This issue causes a complete system hang (CPU stuck for 143s+) and leads to subsequent I/O starvation and system paralysis (e.g., jbd2 and systemd-journald blocked). > > ### Crash Log Snippet > > watchdog: BUG: soft lockup - CPU#3 stuck for 143s! [systemd-udevd:162] > RIP: 0010:ioread32+0x0/0xa0 > Call Trace: > > __ast_read32 > __ast_mindwm+0x4d/0x80 [ast] > ast_2500_patch_ahb+0x9d/0x120 [ast] > ast_detect_chip > ast_pci_probe+0xa1a/0xb70 [ast] > ... > > ### Vulnerability Analysis > > Even on bare-metal hardware, an unresponsive ASPEED chip, a PCIe bus fault, or unexpected hardware states can cause the kernel to hang forever in the following loops during initialization: > > 1. Inside `ast_2500_patch_ahb()`: > do { > __ast_moutdwm(regs, 0x1e6e2000, 0x1688A8A8); > data = __ast_mindwm(regs, 0x1e6e2000); > } while (data != 1); // <--- Infinite loop if hardware doesn't respond properly > > 2. Inside the underlying I/O accessors `__ast_mindwm()` and `__ast_moutdwm()`: > do { > data = __ast_read32(regs, 0xf004) & 0xffff0000; > } while (data != (r & 0xffff0000)); // <--- Infinite loop > > ### Proposed Fix Direction > > To prevent the kernel from hanging indefinitely and to gracefully abort the probe (`-ENODEV`) upon hardware failure, these loops must implement a timeout mechanism (e.g., using `readx_poll_timeout` or a loop counter with `udelay`). > > Interestingly, other functions in the same file (e.g., `mmc_test`) correctly implement a timeout counter (`if (++timeout > TIMEOUT) return false;`), but the initialization paths mentioned above blindly trust the hardware state. > > We are reporting this defect so that the maintainers can decide the appropriate timeout thresholds and implement a safe fallback mechanism across the `ast` driver. > > Please let us know if you need more information or the full dmesg log. Thanks for reporting. Will you send a patch? Best regards Thomas > > Reported-by: Mingyu Wang <25181214217@stu.xidian.edu.cn> > > Best regards, > Mingyu Wang > -- -- Thomas Zimmermann Graphics Driver Developer SUSE Software Solutions Germany GmbH Frankenstr. 146, 90461 Nürnberg, Germany, www.suse.com GF: Jochen Jaser, Andrew McDonald, Werner Knoblich, (HRB 36809, AG Nürnberg)