Hi again, bad news: my previous analysis was completely wrong, c.f. below. Good news (from my point of view): debugfs is correct, no fix needed for it. Apologies for the confusion... Nicolai Stange <nicstange@xxxxxxxxx> writes: > Greg KH <greg@xxxxxxxxx> writes: > >> On Mon, Oct 31, 2016 at 02:32:56PM -0400, Mike Marshall wrote: >> >>> But... really bad things happen if someone unloads the Orangefs >>> module after my test program does the open and before the read >>> starts. So I picked another debugfs-using-filesystem (f2fs) and >>> pointed my tester-program at /sys/kernel/debug/f2fs/status, and >>> the same bad thing happens there. > > [...] > >>> [ 1240.144316] Call Trace: >>> [ 1240.144450] [<ffffffff8122907f>] __fput+0xdf/0x1d0 >>> [ 1240.144704] [<ffffffff812291ae>] ____fput+0xe/0x10 >>> [ 1240.144962] [<ffffffff810b97de>] task_work_run+0x8e/0xc0 >>> [ 1240.145243] [<ffffffff8109b98e>] do_exit+0x2ae/0xae0 > > > Thank you very much for this detailed report! > > At least for the .../f2fs/status file, your splat at fput() can be > readily explained with the full proxy's releaser not being protected > against file removals in any way. > > Partly this is on purpose, c.f. the comment in full_proxy_release(). > > However, I should have at least tried to acquire a reference to the > owning module before accessing some static struct file_operations or > even calling some ->release() within it. Meh. This is what I got wrong: debugfs does acquire the needed references correctly (details below). For the case of f2fs' "status" file, the file_operations ->owner is simply not set as it should have been, i.e. to THIS_MODULE. Details on debugfs' reference acquisition: The open proxy, full_proxy_open(), gets a reference to the "real" file_operations, hence to its module. (Only in its error path it releases it again). full_proxy_release() is in charge of dropping that reference again, but only *after* it has attempted to call the "real" ->release(). So, as long as a file has been (successfully) opened, a reference to the original file_operation's ->owner is owned, preventing it from getting unloaded. Can you confirm that you didn't set ->owner in your Orangefs related tests, too? Thanks, Nicolai -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
