Messages in this thread | | | Date | Thu, 17 Sep 2020 13:48:38 +0100 | From | Matthew Wilcox <> | Subject | Re: [RFC PATCH] locking/percpu-rwsem: use this_cpu_{inc|dec}() for read_count |
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On Thu, Sep 17, 2020 at 02:01:33PM +0200, Oleg Nesterov wrote: > IIUC, file_end_write() was never IRQ safe (at least if !CONFIG_SMP), even > before 8129ed2964 ("change sb_writers to use percpu_rw_semaphore"), but this > doesn't matter... > > Perhaps we can change aio.c, io_uring.c and fs/overlayfs/file.c to avoid > file_end_write() in IRQ context, but I am not sure it's worth the trouble.
If we change bio_endio to invoke the ->bi_end_io callbacks in softirq context instead of hardirq context, we can change the pagecache to take BH-safe locks instead of IRQ-safe locks. I believe the only reason the lock needs to be IRQ-safe is for the benefit of paths like:
mpage_end_io page_endio end_page_writeback test_clear_page_writeback
Admittedly, I haven't audited all the places that call end_page_writeback; there might be others called from non-BIO contexts (network filesystems?). That was the point where I gave up my investigation of why we use an IRQ-safe spinlock when basically all page cache operations are done from user context.
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