Hi, I have a test case on mount/umount on a partition from nfs server side. And encounter a problem of umount busy in a low probability. The Linux version is 3.10.64 with the patch "sunrpc/cache: make cache flushing more reliable". https://patchwork.kernel.org/patch/7410021/ After some analysis and test in many times, I find that when it failed to mount, the time "then" and "now" are different, which caused the last_refresh is far beyond the flush_time. So this cache is not expired and won't be clean at once. Then the ref in cache_head won't be released, and mntput_no_expire didn't be called to decrease the count. That caused the umount busy. Below are logs in my test. kernel: [ 292.767801] write_flush 1480 then = 249, now = 250 kernel: [ 292.767817] cache_clean 451, cd name nfsd.fh expiry_time 790485253, cd flush_time 249, last_refresh 369, seconds_since_boot 250 kernel: [ 292.767913] write_flush 1480 then = 249, now = 250 kernel: [ 292.767928] cache_clean 451, cd name nfsd.export expiry_time 2049, cd flush_time 249, last_refresh 369, seconds_since_boot 250 kernel: [ 292.773229] do_refcount_check 283 mycount 4 kernel: [ 292.773245] do_umount 1344 retval -16 I think this happens in such case that the exportfs writes the flush with current time, the time of "then". But when seconds_since_boot being called in function write_flush, the time is on the next second, so the "now" is one second after "then". Because "then" is less than "now", the flush_time is set directly to original "then", rather than "cd->flush_time + 1". And I want to change the condition as below. I'm not sure it's OK and has no effects to other part. -------------------------------------------------------------------------- then = get_expiry(&bp); now = seconds_since_boot(); cd->nextcheck = now; /* Can only set flush_time to 1 second beyond "now", or * possibly 1 second beyond flushtime. This is because * flush_time never goes backwards so it mustn't get too far * ahead of time. */ if (then != now) printk("%s %d then = %d, now = %d\n", __func__, __LINE__, then, now); - if (then >= now) { + if (then >= now - 1) { /* Want to flush everything, so behave like cache_purge() */ if (cd->flush_time >= now) now = cd->flush_time + 1; then = now; } cd->flush_time = then; -------------------------------------------------------------------------- Best Regards, Alan Wang -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
