Messages in this thread | | | Date | Thu, 05 Apr 2012 17:45:04 +0200 | From | Florian Fainelli <> | Subject | Re: Caching issues with tmpfs? |
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Hi again Hugh,
Le 04/05/12 17:07, Florian Fainelli a écrit : > Hi Hugh, > > I am encountering a very weird and serious issue with tmpfs, which I > have seen both in 2.6.39 and 3.2.13. The issue is the following: > > 1) I read a file from a NAND device back to /tmp/bar > 2) /tmp/bar is loopback mounted to /tmp/bar_mount/ > 3) when I list the contents of /tmp/bar_mount I see only half of my > files, and using hexdump on /tmp/bar shows that the cramfs header is > correct and contains all, which rules out the cramfs issue > 4) if I move /tmp/bar to /tmp/bar.move and loopback mount /tmp/bar.move > to /tmp/bar_mount, I now see all the files present > > I have compared the md5sums of the cramfs file before mounting, after > mounting, before moving, after moving, they are all the same. Also, the > loopback mount does not yiel when mounting the cramfs file, which rules > out its bad integrity. > > the /tmp directory is mounted with the defaults attributes (rw,relatime). > > My system is a x86 Atom-based System-on-a-Chip and should not suffer > from the CPU data cache aliasing issue mentioned here: > http://lkml.indiana.edu/hypermail/linux/kernel/1202.0/00090.html > > I backported this patch however, and it does not make any difference as > expected. > > This behavior has been observed on several devices. > > I will try to provide you with a test case to reproduce the issue, > meanwhile any hints are appreciated :)
I am terribly sorry for suspecting tmpfs, the issue is actually in busybox, which is smart enough not to delete the loop device after an umount and keep a stale copy of the file used as source. Consequent mounts are then given the same stale copy because the name of the source file matches the non-deleted loopback setup. -- Florian -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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