Re: [Crash-utility] [PATCH] Fix the "kmem -s" option for Linux 5.7 and later kernels
Hi Lianbo,
No, the patch fixes the above errors. Upstream kernel has changed
the calculation formula in the
freelist_ptr() as below(marked it with "^^^^"), which added the
"swab()" operation, crash also needs
to follow up this change, otherwise crash will get the error of "invalid
freepointer".
Before:
crash> kmem -s
CACHE OBJSIZE ALLOCATED TOTAL SLABS SSIZE NAME
c0000000311a4200 152 0 0 0 64k fuse_request
c0000000311a8700 800 0 0 0 64k fuse_inode
c000000035df7600 528 0 0 0 64k xfs_dqtrx
c000000035df6600 496 0 0 0 64k xfs_dquot
kmem: xfs_buf: slab: c00c0000000b6500 invalid freepointer: 3808942d00004eb0
kmem: xfs_buf: slab: c00c00000116ba00 invalid freepointer: b83fe85a040027b0
...
Yes, you are right, and thanks for the info.
I was confused because I could not reproduce the error message with a dozen
vmcores.
With some debugging, I think maybe the message itself does not occur on x86_64
due to this issue, because get_freepointer() returns a value having 1 in bit 1
on x86_64 and breaks the loop below.
@@ -19361,6 +19361,7 @@ get_freepointer(struct meminfo *si, void *object)
return BADADDR;
}
+ fprintf(fp, "DEBUG: vaddr: %lx ptr: %lx\n", vaddr,
freelist_ptr(si,nextfree,vaddr));
return (freelist_ptr(si, nextfree, vaddr));
}
crash> kmem -s
CACHE OBJSIZE ALLOCATED TOTAL SLABS SSIZE NAME
...
DEBUG: vaddr: ffff927b0501b5b8 ptr: b8b501057b92ec47
DEBUG: vaddr: ffff927b05221bb8 ptr: b81b22057b92f8c7
DEBUG: vaddr: ffff927b05218e38 ptr: 388e21057b92f647
DEBUG: vaddr: ffff927b052269b8 ptr: b86922057b92f647
^bit1 = 1
ffff927b08452200 360 802 840 40 8k xfs_buf
DEBUG: vaddr: ffff927b07991900 ptr: 1999077b92f1f7
DEBUG: vaddr: ffff927b017ac130 ptr: 30c17a017b92f017
DEBUG: vaddr: ffff927b0496d9c8 ptr: c8d996047b92fcc7
DEBUG: vaddr: ffff927b01bce5e0 ptr: e0e5bc017b92f37f
ffff927b08452b00 200 50 480 24 4k xfs_bui_item
for (q = freelist; q; q = get_freepointer(si, (void *)q)) {
if (q & PAGE_MAPPING_ANON)
break; <<-- break here
However, the issue affects the calculation of allocated/free objects
also on x86_64:
-ffff927b08452200 360 802 840 40 8k xfs_buf
+ffff927b08452200 360 777 840 40 8k xfs_buf
^^^
> > Linux 5.7 and later kernels that contain kernel commit
<1ad53d9fa3f6>
> > ("slub: improve bit diffusion for freelist ptr obfuscation")
changed
> > the calculation formula in the freelist_ptr(), which added a swab()
> > call to mix bits a little more. When kernel is built with the
> > "CONFIG_SLAB_FREELIST_HARDENED=y",the "kmem -s" option
fails with the
> > following errors, if there is no such patch.
So, could I change the latter part of the commit message to the following?
When kernel is configured with the "CONFIG_SLAB_FREELIST_HARDENED=y",
Without the patch, the "kmem -s|-S" option displays wrong statistics and
state whether the slab objects are in use or free and can print the
following errors.
Thanks,
Kazu