On Feb 14, 2026 / 13:43, Yu Kuai wrote: > Creating debugfs entries can trigger fs reclaim, which can enter back > into the block layer request_queue. This can cause deadlock if the > queue is frozen. > > Previously, a WARN_ON_ONCE check was used in debugfs_create_files() > to detect this condition, but it was racy since the queue can be frozen > from another context at any time. > > Introduce blk_debugfs_lock()/blk_debugfs_unlock() helpers that combine > the debugfs_mutex with memalloc_noio_save()/restore() to prevent fs > reclaim from triggering block I/O. Also add blk_debugfs_lock_nomemsave() > and blk_debugfs_unlock_nomemrestore() variants for callers that don't > need NOIO protection (e.g., debugfs removal or read-only operations). > > Replace all raw debugfs_mutex lock/unlock pairs with these helpers, > using the _nomemsave/_nomemrestore variants where appropriate. > > Reported-by: Yi Zhang <[email protected]> > Closes: > https://lore.kernel.org/all/CAHj4cs9gNKEYAPagD9JADfO5UH+OiCr4P7OO2wjpfOYeM-RV=a...@mail.gmail.com/ > Reported-by: Shinichiro Kawasaki <[email protected]> > Closes: https://lore.kernel.org/all/aYWQR7CtYdk3K39g@shinmob/ > Suggested-by: Christoph Hellwig <[email protected]> > Signed-off-by: Yu Kuai <[email protected]>
Yu, thank you for fixing this. I applied this patch on top of the kernel next-20260211 and confirmed that the WARN is no longer reported for the test case zbd/012. I also ran whole blktests and observed no regression. Tested-by: Shinichiro Kawasaki <[email protected]>
