1 内核打点

echo 'r:pread64_ret ksys_pread64 ret=$retval:s64' > kprobe_events
echo 'ret < 0' > events/kprobes/pread64_ret/filter

echo 1 > events/kprobes/pread64_ret/enable

echo 'r:xfs_file_read_iter xfs_file_read_iter ret=$retval:s64' >> kprobe_events
echo 'ret < 0' > events/kprobes/xfs_file_read_iter/filter
echo 1 > events/kprobes/xfs_file_read_iter/enable

echo 'r:generic_file_buffered_read generic_file_buffered_read ret=$retval:s64' >> kprobe_events
echo 'ret < 0' > events/kprobes/generic_file_buffered_read/filter
echo 1 > events/kprobes/generic_file_buffered_read/enable

echo 'r:rw_verify_area rw_verify_area ret=$retval:s32' >> kprobe_events
echo 'ret < 0' > events/kprobes/rw_verify_area/filter
echo 1 > events/kprobes/rw_verify_area/enable

echo 'error != 0' > events/block/block_rq_complete/filter
echo 1 > events/block/block_rq_complete/enable
echo 'r:ondemand_readahead ondemand_readahead ret=$retval:s64' >> kprobe_events

echo 'ret < 0' > events/kprobes/ondemand_readahead/filter
echo 1 > events/kprobes/ondemand_readahead/enable
echo 'r:read_pages read_pages ret=$retval:s32' >> kprobe_events
echo 'ret < 0' > events/kprobes/read_pages/filter再次复现时结果如下：

echo 1 > events/kprobes/read_pages/enable
echo 'r:iomap_apply iomap_apply ret=$retval:s64' >> kprobe_events
echo 'ret < 0' > events/kprobes/iomap_apply/filter
echo 1 > events/kprobes/iomap_apply/enable
echo 'r:iomap_readpage_actor iomap_readpage_actor ret=$retval:s64' >>
kprobe_events
echo 'ret < 0' > events/kprobes/iomap_readpage_actor/filter
echo 1 > events/kprobes/iomap_readpage_actor/enable

static ssize_t generic_file_buffered_read(struct kiocb *iocb,
struct iov_iter *iter, ssize_t written)
{
......
readpage:
/*
┊* A previous I/O error may have been due to temporary
┊* failures, eg. multipath errors.
┊* PG_error will be set again if readpage fails.
┊*/
ClearPageError(page);
/* Start the actual read. The read will unlock the page. */
error = mapping->a_ops->readpage(filp, page); --> 读page ok
if (unlikely(error)) {
if (error == AOP_TRUNCATED_PAGE) {
put_page(page);
error = 0;
goto find_page;
}
goto readpage_error;
}
if (!PageUptodate(page)) { --> page没有置上uptodate标记
error = lock_page_killable(page); --> 锁page
if (unlikely(error))
goto readpage_error;
if (!PageUptodate(page)) {
if (page->mapping == NULL) { --> page的
mapping还在
/*
┊* invalidate_mapping_pages got it
┊*/
unlock_page(page);
put_page(page);因此推测问题原因是xfs_vm_readpage没有报错，但是没有给page置上uptodate标记，继续看设置
uptodate标记的地方：
goto find_page;
}
unlock_page(page);
shrink_readahead_size_eio(filp, ra);
error = -EIO; --> 返回-EIO
goto readpage_error;
}
unlock_page(page);
}
goto page_ok;
......
}