Messages in this thread | | | Date | Wed, 1 Jul 2009 17:12:49 -0700 | From | Andrew Morton <> | Subject | Re: [RESEND Patch] kcore: remove its pointless size |
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On Wed, 01 Jul 2009 16:25:05 -0700 ebiederm@xmission.com (Eric W. Biederman) wrote:
> Andrew Morton <akpm@linux-foundation.org> writes: > > >> index 59b43a0..eca5201 100644 > >> --- a/fs/proc/kcore.c > >> +++ b/fs/proc/kcore.c > >> @@ -405,9 +405,6 @@ read_kcore(struct file *file, char __user *buffer, size_t buflen, loff_t *fpos) > >> static int __init proc_kcore_init(void) > >> { > >> proc_root_kcore = proc_create("kcore", S_IRUSR, NULL, &proc_kcore_operations); > >> - if (proc_root_kcore) > >> - proc_root_kcore->size = > >> - (size_t)high_memory - PAGE_OFFSET + PAGE_SIZE; > >> return 0; > >> } > >> module_init(proc_kcore_init); > > > > AFAICT this means that proc_root_kcore->size will remain uninitialised > > until a process opens and reads from /proc/kcore. So on initial boot > > the `ls' output will presumably show a size of zero, and this will > > change once /proc/kcore has been read? > > Which is better than showing a random number of dubious relationship > to the size we normally show. That code is just a maintenance problem.
Well it's not just that st_size is wrong before the first read. It's also wrong after memory hot-add, up until the next read.
> > If so, should we run get_kcore_size() in proc_kcore_init(), perhaps? > > > > In fact, do we need to run get_kcore_size() more than once per boot? > > > > AFAICT we only run kclist_add() during bootup, so if proc_kcore_init() > > is called at the appropriate time, we can permanently cache its result? > > > > In which case get_kcore_size() and kclist_add() can be marked __init. > > > > Maybe that's all wrong - I didn't look terribly closely. > > Memory hot add I expect is the excuse. There is more that could be > done. But this patch is an obvious bit of chipping away nonsense > code.
We have the infrastructure to get this right, I think:
- run
proc_root_kcore->size = get_kcore_size(...)
within proc_kcore_init()
- register a memory-hotplug notifier and each time memory goes online or offline, rerun
proc_root_kcore->size = get_kcore_size(...)
- stop running get_kcore_size() within read_kcore().
I suspect that read_kcore() will not behave well if a memory hotplug operation happens concurrently. But that's a separate problem.
(hopefully cc's some memory-hotplug people)
Or we just leave /proc/kcore's st_size at zero. It's a pretty hopeless exercise trying to get this "right", as nobody can safely _use_ that size - it can be wrong as soon as the caller has read from it.
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