Messages in this thread | | | From | Mariusz Kozlowski <> | Subject | Re: 2.6.24-rc5-mm1: problems with cat /proc/kpageflags | Date | Mon, 17 Dec 2007 20:05:37 +0100 |
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Hello,
> > cat /proc/kpagecount on the other hand - with the change in line 710 > > - locks the box. Sysrq works, changing consoles works, but there is > > no "BUG: soft lockup ..." message. After a while the box becomes > > totaly unresponsive - even caps lock doesn't work, no responses to > > ping. > > Well I'm baffled. There's basically two things in that function that > do anything interesting: pfn_to_page and put_user. access_ok is > "return 1" on Sparc64. atomic_read is a simple read. > > My usual approach at this point would be to litter it with printks and > see where its hanging.
Ok. Maybe this will help. Don't know how to compare that to the results from yesterday (test with ppage = NULL) - maybe I f.... something up. This time I added a bunch of printks and got these results:
This is from 'cat /proc/kpageflags' (after this the box is locked):
01 pfn:0, src:0, KPMSIZE:8 23458 ppage:0000000200000000, pfn:1
and the relevant code:
static ssize_t kpageflags_read(struct file *file, char __user *buf, size_t count, loff_t *ppos) {
u64 __user *out = (u64 __user *)buf; struct page *ppage; unsigned long src = *ppos; unsigned long pfn; ssize_t ret = 0; u64 kflags, uflags;
printk("0");
if (!access_ok(VERIFY_WRITE, buf, count)) return -EFAULT;
printk("1"); pfn = src / KPMSIZE; printk("\npfn:%u, src:%u, KPMSIZE:%d\n", pfn, src, KPMSIZE); count = min_t(unsigned long, count, (max_pfn * KPMSIZE) - src);
printk("2"); if (src & KPMMASK || count & KPMMASK) return -EIO;
printk("3"); while (count > 0) { printk("4"); ppage = pfn_to_page(pfn++); printk("5"); if (!ppage) { printk("6"); kflags = 0; printk("7"); } else { printk("8"); printk("\nppage:%p, pfn:%u\n", ppage, pfn); kflags = ppage->flags; // <---------------- something bad happens printk("9"); }
printk("a");
This is from 'cat /proc/kpagecount' (after this the box is locked)
01 pfn:0, src:0, KPMSIZE:8 23567a ppage:0000000200000000, pfn:1
and this is the relevant code:
static ssize_t kpagecount_read(struct file *file, char __user *buf, size_t count, loff_t *ppos) {
u64 __user *out = (u64 __user *)buf; struct page *ppage; unsigned long src = *ppos; unsigned long pfn; ssize_t ret = 0; u64 pcount; printk("0"); if (!access_ok(VERIFY_WRITE, buf, count)) return -EFAULT;
printk("1"); pfn = src / KPMSIZE; printk("\npfn:%u, src:%u, KPMSIZE:%d\n", pfn, src, KPMSIZE);
printk("2"); count = min_t(size_t, count, (max_pfn * KPMSIZE) - src); printk("3"); if (src & KPMMASK || count & KPMMASK) {
printk("4"); return -EIO; } printk("5"); while (count > 0) { printk("6"); ppage = pfn_to_page(pfn++); printk("7"); if (!ppage) { printk("8"); pcount = 0; } else { printk("a"); printk("\nppage:%p, pfn:%u\n", ppage, pfn); pcount = atomic_read(&ppage->_count); // <---------------- something bad happens printk("b"); }
Regards,
Mariusz
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