Re: [PATCH v4] mm: per-thread vma caching

[Davidlohr Bueso]

On Mon, 2014-03-03 at 19:26 -0800, Linus Torvalds wrote:
> On Mon, Mar 3, 2014 at 7:13 PM, Davidlohr Bueso <davidlohr@xxxxxx> wrote:
> >
> > Yes, I shortly realized that was silly... but I can say for sure it can
> > happen and a quick qemu run confirms it. So I see your point as to
> > asking why we need it, so now I'm looking for an explanation in the
> > code.
> 
> We definitely *do* have users.
> 
> One example would be ptrace -> access_process_vm -> __access_remote_vm
> -> get_user_pages() -> find_extend_vma() -> find_vma_prev -> find_vma.

And:

[    4.274542] Call Trace:
[    4.274747]  [<ffffffff81809525>] dump_stack+0x46/0x58
[    4.275069]  [<ffffffff811331ee>] vmacache_find+0xae/0xc0
[    4.275425]  [<ffffffff8113c840>] find_vma+0x20/0x80
[    4.275625]  [<ffffffff8113e5cb>] find_extend_vma+0x2b/0x90
[    4.275982]  [<ffffffff81138a09>] __get_user_pages+0x99/0x5a0
[    4.276427]  [<ffffffff81137b0b>] ? follow_page_mask+0x32b/0x400
[    4.276671]  [<ffffffff81138fc2>] get_user_pages+0x52/0x60
[    4.276886]  [<ffffffff81167dc3>] copy_strings.isra.20+0x1a3/0x2f0
[    4.277239]  [<ffffffff81167f4d>] copy_strings_kernel+0x3d/0x50
[    4.277472]  [<ffffffff811b3688>] load_script+0x1e8/0x280
[    4.277692]  [<ffffffff81167d0a>] ? copy_strings.isra.20+0xea/0x2f0
[    4.277931]  [<ffffffff81167ff7>] search_binary_handler+0x97/0x1d0
[    4.278288]  [<ffffffff811694bf>] do_execve_common.isra.28+0x4ef/0x650
[    4.278544]  [<ffffffff81169638>] do_execve+0x18/0x20
[    4.278754]  [<ffffffff8116984e>] SyS_execve+0x2e/0x40
[    4.278960]  [<ffffffff8181b549>] stub_execve+0x69/0xa0


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