Messages in this thread | | | Date | Tue, 5 Dec 2017 10:41:50 +0100 | From | Jan Kara <> | Subject | Re: possible deadlock in generic_file_write_iter (2) |
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Hello Byungchul,
On Tue 05-12-17 13:58:09, Byungchul Park wrote: > On 12/4/2017 5:33 PM, Jan Kara wrote: > >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:
OK, thanks for the tip.
> 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.
But this is something I don't get: There aren't sb_writers anywhere near put_ucounts(). So why the heck did lockdep think that sb_writers are acquired by put_ucounts()?
Honza -- Jan Kara <jack@suse.com> SUSE Labs, CR
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