On Wed, Jun 30, 2021 at 10:09 AM www <ouyangxua...@163.com> wrote: > Dear all, > > systemd version: v234 > kernel version: 5.1.5 > > My embedded system uses systemd. Occasionally kernel panic appears in this > system. It is found that it is related to sd-sync in systemd. How to > analyze this and why? > What causes this problem? Or can you see that sd-sync has a problem > processing that file or service? > If you have any ideas or opinions, or need any specific information, > please let me know. > > Thank you. > > [ 1664.582102] Unable to handle kernel paging request at virtual address > 7f8bba1c > [ 1664.589350] pgd = fb46e47e > [ 1664.592062] [7f8bba1c] *pgd=00000000 > [ 1664.595666] Internal error: Oops: 80000005 [#1] ARM > [ 1664.600558] CPU: 0 PID: 14730 Comm: (*sd-sync*) Not tainted > 5.1.5-yocto-s-dirty-fd96c2b #1 >
When shutdown.target is invoked, systemd forks a 'sd-sync' background process which does literally one thing: it issues a global sync() to begin flushing all filesystems to disk. There is no specific file involved here, sync() handles all mounted filesystems at once. Check what happens if you run `/usr/sbin/sync` from shell, since it does exactly the same thing. In general there should be nothing special about systemd calling sync(), it's purely a kernel problem. The only difference that I can think of is that systemd begins the sync() while all services are shutting down and still actively writing to files... -- Mantas Mikulėnas
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