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Warner Losh authored
The vast majority of the busy/unbusy users in the tree don't acquire Giant before calling device_busy/unbusy. However, if multiple threads are opening a file, say, that causes the device to busy/unbusy, then we can race to the root marking things busy. Create a new device_busy_locked and device_unbusy_locked that are the current implemntations of device_busy and device_unbusy. Make device_busy and unbusy acquire Giant before calling the _locked versrions. Since we never sleep in the busy/unbusy path, Giant's single threaded semantics suffice to keep this safe. Sponsored by: Netflix Reviewed by: hselasky, jhb Differential Revision: https://reviews.freebsd.org/D26284
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