On Tue, Dec 05, 2017 at 10:19:07AM +0100, Dmitry Vyukov wrote: > On Tue, Dec 5, 2017 at 5:58 AM, Byungchul Park <byungchul.park@xxxxxxx> wrote: > > On 12/4/2017 5:33 PM, Jan Kara wrote: > >> > >> Hello, > >> > >> adding Peter and Byungchul to CC since the lockdep report just looks > >> strange and cross-release seems to be involved. Guys, how did #5 get into > >> the lock chain and what does put_ucounts() have to do with sb_writers > >> there? Thanks! > > > > > > Hello Jan, > > > > In order to get full stack of #5, we have to pass a boot param, > > "crossrelease_fullstack", to the kernel. Now that it only informs > > put_ucounts() in the call trace, it's hard to find out what exactly > > happened at that time, but I can tell #5 shows: > > > > When acquire(sb_writers) in put_ucounts(), it was on the way to > > complete((completion)&req.done) of wait_for_completion() in > > devtmpfs_create_node(). > > > > If acquire(sb_writers) in put_ucounts() is stuck, then > > wait_for_completion() in devtmpfs_create_node() would be also > > stuck, since complete() being in the context of acquire(sb_writers) > > cannot be called. > > > > This is why cross-release added the lock chain. > > Hi, > > What is cross-release? Is it something new? Should we always enable > crossrelease_fullstack during testing? Hello Dmitry, Yes, it's new one making lockdep track wait_for_completion() as well. And we should enable crossrelease_fullstack if you don't care system slowdown but testing. -- Thanks, Byungchul -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
