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Sun, 26 Jul 2026 12:11:31 +0800 (CST) X-Sender: hdanton@sina.com X-Auth-ID: hdanton@sina.com Authentication-Results: sina.com; spf=none smtp.mailfrom=hdanton@sina.com; dkim=none header.i=none; dmarc=none action=none header.from=hdanton@sina.com X-SMAIL-MID: 9337046685618 X-SMAIL-UIID: 5EDBA19B5CFB4B9481344B454EA678DE-20260726-121131-1 From: Hillf Danton To: syzbot Cc: linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com Subject: Re: [syzbot] [input?] possible deadlock in tasklet_action_common (2) Date: Sun, 26 Jul 2026 12:11:08 +0800 Message-ID: <20260726041120.754-1-hdanton@sina.com> In-Reply-To: <6a655704.70955b6c.323240.0028.GAE@google.com> References: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit > Date: Sat, 25 Jul 2026 17:38:28 -0700 [thread overview] > syzbot has found a reproducer for the following issue on: > > HEAD commit: cc2b5f627e8c Add linux-next specific files for 20260714 > git tree: linux-next > console output: https://syzkaller.appspot.com/x/log.txt?x=13d446b9580000 > kernel config: https://syzkaller.appspot.com/x/.config?x=2290ccbf984c524f > dashboard link: https://syzkaller.appspot.com/bug?extid=b5d7ab56d43de3fd5aac > compiler: Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8 > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1310a232580000 > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=13c3b2ea580000 #syz test --- x/kernel/softirq.c +++ y/kernel/softirq.c @@ -924,7 +924,6 @@ static void tasklet_action_common(struct tl_head->tail = &tl_head->head; local_irq_enable(); - tasklet_lock_callback(); while (list) { struct tasklet_struct *t = list; @@ -944,7 +943,6 @@ static void tasklet_action_common(struct } } tasklet_unlock(t); - tasklet_callback_sync_wait_running(); continue; } tasklet_unlock(t); @@ -957,7 +955,6 @@ static void tasklet_action_common(struct __raise_softirq_irqoff(softirq_nr); local_irq_enable(); } - tasklet_unlock_callback(); } static __latent_entropy void tasklet_action(void) @@ -1006,11 +1003,10 @@ void tasklet_unlock_spin_wait(struct tas while (test_bit(TASKLET_STATE_RUN, &(t)->state)) { if (IS_ENABLED(CONFIG_PREEMPT_RT)) { /* - * Prevent a live lock when current preempted soft - * interrupt processing or prevents ksoftirqd from - * running. + * wait_on_bit(TASKLET_STATE_RUN) + * https://lore.kernel.org/lkml/20260524004526.1046-1-hdanton@sina.com/ */ - tasklet_callback_cancel_wait_running(); + tasklet_unlock_wait(t); } else { cpu_relax(); } --- x/drivers/gpu/drm/drm_mode_config.c +++ y/drivers/gpu/drm/drm_mode_config.c @@ -869,8 +869,7 @@ static void validate_blend_mode_for_alph for (i = 0; i < plane->format_count; i++) { fmt = drm_format_info(plane->format_types[i]); if (fmt->has_alpha) { - WARN(1, "[PLANE:%d:%s] pixel format with alpha exposed but blend mode not setup", - plane->base.id, plane->name); + pr_err("[PLANE:%d:%s] pixel format with alpha exposed but blend mode not setup\n", plane->base.id, plane->name); break; } } --