On Apr 17, 2015, at 9:01 PM, Al Viro <viro@xxxxxxxxxxxxxxxxxx> wrote: > > On Mon, Mar 23, 2015 at 01:37:38PM +1100, NeilBrown wrote: >> lustre's ->follow_link() uses a lot of stack space and so >> need to limit symlink recursion based on stack size. >> >> It currently tests current->link_count, but that will soon >> become private to fs/namei.c. >> So instead base on actual available stack space. >> This patch aborts recursive symlinks in less than 2K of space >> is available. This seems consistent with current code, but >> hasn't been tested. > > BTW, in the best case that logics is fishy. We have "up to 5 levels with > 4Kb stack and up to 7 with 8Kb one". Could somebody manage to dig out > the reasons for such limits? Preferably along with the kernel version > where the overflows had been observed, both for 4K and 8K cases. Hi Al, I checked in our bug history, and the 8KB stack limit was hit with older clients running racer or our recursive-symlink regression test: 2.6.18: https://bugzilla.lustre.org/show_bug.cgi?id=18533#c0 2.6.16: https://bugzilla.lustre.org/show_bug.cgi?id=19380#c11 The 4KB stack limit for clients has existed a lot longer than that, but CONFIG_4KSTACKS was not the default on all kernels for a while. The following bug showed a stack overflow with 2.6.22 kernels: https://bugzilla.lustre.org/show_bug.cgi?id=17379#c0 Prior to 2.6.16 when we needed client-side kernel patches and a custom kernel build, we always forced the CONFIG_4KSTACKS off in the config. In general, Lustre is a heavy stack user because it is a network filesystem, and doubly so if the Lustre client is re-exporting the filesystem to NFS clients. I'd be happy if symlink recursion was removed completely, but so far the added symlink recursion limit hasn't been a problem for Lustre users. Cheers, Andreas -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
