Messages in this thread | | | Date | Fri, 18 Aug 2023 22:23:36 +0200 | Subject | Re: ARM board lockups/hangs triggered by locks and mutexes | From | Rafał Miłecki <> |
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On 14.08.2023 11:04, Geert Uytterhoeven wrote: > Hi Rafal, > > On Mon, Aug 7, 2023 at 1:11 PM Rafał Miłecki <zajec5@gmail.com> wrote: >> On 4.08.2023 13:07, Rafał Miłecki wrote: >>> I triple checked that. Dropping a single unused function breaks kernel / >>> device stability on BCM53573! >>> >>> AFAIK the only thing below diff actually affects is location of symbols >>> (I actually verified that by comparing System.map before and after - >>> over 22'000 of relocated symbols). >>> >>> Can some unfortunate location of symbols cause those hangs/lockups? >> >> I performed another experiment. First I dropped mtd_check_of_node() to >> bring kernel back to the stable state. >> >> Then I started adding useless code to the mtdchar_unlocked_ioctl(). I >> ended up adding just enough to make sure all post-mtd symbols in >> System.map got the same offset as in case of backporting >> mtd_check_of_node(). >> >> I started experiencing lockups/hangs again. >> >> I repeated the same test with adding dumb code to the brcm_nvram_probe() >> and verifying symbols offsets following brcm_nvram_probe one. >> >> I believe this confirms that this problem is about offset or alignment >> of some specific symbol(s). The remaining question is what symbols and >> how to fix or workaround that. > > I had similar experiences on other ARM platforms many years ago: > bisection lead to something completely bogus, and it turned out > adding a single line of innocent code made the system lock-up or crash > unexpectedly. It was definitely related to alignment, as adding the > right extra amount of innocent code would fix the problem. Until some > later change changing alignment again... > I never found the real cause, but the problems went away over time. > I am not sure I did enable all required errata config options, so I > may have missed some...
I already experiented some weird performance variations on Broadcom's Northstar platform that was related to symbols layout & cache hit/miss ratio. For that reason I use -falign-functions=32 for that whole OpenWrt's "bcm53xx" target (it covers Northstar and BCM53573). So this aspect should be ruled out already in my case.
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