lkml.org 
[lkml]   [2012]   [Feb]   [16]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: hugetlbfs lockdep spew revisited.
On Thu, Feb 16, 2012 at 07:08:57PM -0500, Dave Jones wrote:
> Remember this ? https://lkml.org/lkml/2011/4/15/272
> Josh took a stab at fixing it in e096d0c7e2e4e5893792db865dd065ac73cf1f00,
> but it seems to still be there.

> the existing dependency chain (in reverse order) is:

[snip]

... and as bloody usual, that mentioning of readdir in the output is a
red herring; the real problem (and yes, it *is* deadlock-prone) is not
with getdents(2) that cannot happen on anything that could be mmaped;
it's with hugetlbfs_read() (i.e. read(2)) that very definitely *can*.

This is *not* a misannotation and not a false positive; this is a real,
honest deadlock.
Thread A:
read() on hugetlbfs
hugetlbfs_read() called
i_mutex grabbed
hugetlbfs_read_actor() called
__copy_to_user() called
page fault is triggered
Thread B, sharing address space with A:
mmap() the same file
->mmap_sem is grabbed on task_B->mm->mmap_sem
hugetlbfs_file_mmap() is called
attempt to grab ->i_mutex and block waiting for A to give it up
Thread A:
pagefault handled blocked on attempt to grab task_A->mm->mmap_sem,
which happens to be the same thing as task_B->mm->mmap_sem. Block waiting
for B to give it up.

Deadlock.


\
 
 \ /
  Last update: 2012-02-17 01:29    [W:0.100 / U:0.400 seconds]
©2003-2014 Jasper Spaans. Advertise on this site