On Wed, Dec 6, 2017 at 6:05 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. I've enabled CONFIG_BOOTPARAM_LOCKDEP_CROSSRELEASE_FULLSTACK. It should have the same effect, right? -- 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>
