On 02/08/2014 03:06 PM, Linus Torvalds wrote: > On Sat, Feb 8, 2014 at 11:58 AM, Richard Yao <r...@gentoo.org> wrote: >> >> My apologies for that. Here is the backtrace: >> >> [<ffffffff814878ce>] p9_virtio_zc_request+0x45e/0x510 >> [<ffffffff814814ed>] p9_client_zc_rpc.constprop.16+0xfd/0x4f0 >> [<ffffffff814839dd>] p9_client_read+0x15d/0x240 >> [<ffffffff811c8440>] v9fs_fid_readn+0x50/0xa0 >> [<ffffffff811c84a0>] v9fs_file_readn+0x10/0x20 >> [<ffffffff811c84e7>] v9fs_file_read+0x37/0x70 >> [<ffffffff8114e3fb>] vfs_read+0x9b/0x160 >> [<ffffffff81153571>] kernel_read+0x41/0x60 >> [<ffffffff810c83ab>] copy_module_from_fd.isra.34+0xfb/0x180 > > So copy_module_from_fd() does read into a vmalloc'ed buffer (which > isn't pretty, but at least it's not like using some statically > allocated module data), but that's a regular vmalloc() afaik. > > So I don't see the need for "is_vmalloc_or_module_addr()". The regular > "is_vmalloc_addr()" should be fine, and *is* usable from modules (it's > inline, not exported, but it comes to the same thing wrt module use), > exactly because we have traditionally allowed vmalloc'ed memory to be > used. > > So is there some reason why it's not just using that simpler function?
My first instinct was to use "is_vmalloc_addr()" as you suggest.
However, is_vmalloc_addr() only applies to the vmalloc region. While all
architectures load kernel modules into virtual memory (to my knowledge),
some architectures do not load them into the vmalloc region.
is_vmalloc_or_module_addr() contains a comment that clearly states this:
int is_vmalloc_or_module_addr(const void *x)
{
/*
* ARM, x86-64 and sparc64 put modules in a special place,
* and fall back on vmalloc() if that fails. Others
* just put it in the vmalloc space.
*/
#if defined(CONFIG_MODULES) && defined(MODULES_VADDR)
unsigned long addr = (unsigned long)x;
if (addr >= MODULES_VADDR && addr < MODULES_END)
return 1;
#endif
return is_vmalloc_addr(x);
}
My inspection of the actual code agreed with that comment (at least for
S390), so I decided against using "is_vmalloc_addr()" here.
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