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Joanne Koong <joannelkoong@gmail.com> says: This is a fix for this scenario: ->read_folio() gets called on a folio size that is 16k while the file is 4k: a) ifs->read_bytes_pending gets initialized to 16k b) ->read_folio_range() is called for the 4k read c) the 4k read succeeds, ifs->read_bytes_pending is now 12k and the 0 to 4k range is marked uptodate d) the post-eof blocks are zeroed and marked uptodate in the call to iomap_set_range_uptodate() e) iomap_set_range_uptodate() sees all the ranges are marked uptodate and it marks the folio uptodate f) iomap_read_end() gets called to subtract the 12k from ifs->read_bytes_pending. it too sees all the ranges are marked uptodate and marks the folio uptodate using XOR g) the XOR call clears the uptodate flag on the folio The same situation can occur if the last range read for the folio is done as an inline read and all the previous ranges have already completed by the time the inline read completes. For more context, the full discussion can be found in [1]. There was a discussion about alternative approaches in that thread, but they had more complications. There is another discussion in v1 [2] about consolidating the read paths. Until that is resolved, this patch fixes the issue. [1] https://lore.kernel.org/linux-fsdevel/CAJnrk1Z9za5w4FoJqTGx50zR2haHHaoot1KJViQyEHJQq4=34w@mail.gmail.com/#t [2] https://lore.kernel.org/linux-fsdevel/20260219003911.344478-1-joannelkoong@gmail.com/T/#u * patches from https://patch.msgid.link/20260303233420.874231-1-joannelkoong@gmail.com: iomap: don't mark folio uptodate if read IO has bytes pending Link: https://patch.msgid.link/20260303233420.874231-1-joannelkoong@gmail.com Signed-off-by: Christian Brauner <brauner@kernel.org>
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