On Thu, 18 Apr 2024 21:29:57 +0200, Helge Deller wrote: > > On 4/18/24 16:26, Takashi Iwai wrote: > > On Thu, 18 Apr 2024 16:06:52 +0200, > > Nam Cao wrote: > >> > >> On 2024-04-18 Harshit Mogalapalli wrote: > >>> While fuzzing 5.15.y kernel with Syzkaller, we noticed a INFO: task hung > >>> bug in fb_deferred_io_work() > >> > >> Which framebuffer device are you using exactly? It is possible that > >> the problem is with the device driver, not core framebuffer. > > > > Note that it was already known that using flush_delayed_work() caused > > a problem. See the thread of the fix patch: > > https://lore.kernel.org/all/20230129082856.22113-1-tiwai@xxxxxxx/ > > Harshit reported the hung tasks with kernel v5.15-stable, and can even reproduce > that issue with kernel v6.9-rc4 although it has all of your patches from > that referenced mail thread applied. > So, what does your statement that "it was already known that it causes problems" exactly mean? > Can it be fixed? Is someone looking into fixing it? My original fix was intentionally with cancel_delayed_work_sync() because flush_delayed_work() didn't work. We knew that it'd miss some last-minute queued change, but it's better than crash, so it was applied in that way. Then later on, the commit 33cd6ea9c067 changed cancel_*() to flush_delayed_work() blindly, and the known problem resurfaced again. Takashi
