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Debugging a Superblock Percpu_rw_semaphore Deadlock


There are many ways you can go about analyzing a kernel deadlock. While some prefer using lockdep, I find it easier to analyze a kernel dump file.

Judging by the backtrace, the snapshot removal, initiated from veeamblksnap kernel module, got stuck trying to freeze the superblock. io_uring is a complicated beast, and I am not familiar with its code base, and, at this point, I decided to search the LKML, maybe someone else has already reported this deadlock in io_uring. To my surprise, Peter Mann has run into the same issue just a month ago, and Jens Axboe has already fixed it upstream.

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