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author | Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com> | 2012-03-21 16:34:08 -0700 |
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committer | Linus Torvalds <torvalds@linux-foundation.org> | 2012-03-21 17:54:58 -0700 |
commit | a05b0855fd15504972dba2358e5faa172a1e50ba (patch) | |
tree | f4cba4ef12d888ec472714f67ef7bcec318a5191 /mm/filemap.c | |
parent | f5bf18fa22f8c41a13eb8762c7373eb3a93a7333 (diff) | |
download | op-kernel-dev-a05b0855fd15504972dba2358e5faa172a1e50ba.zip op-kernel-dev-a05b0855fd15504972dba2358e5faa172a1e50ba.tar.gz |
hugetlbfs: avoid taking i_mutex from hugetlbfs_read()
Taking i_mutex in hugetlbfs_read() can result in deadlock with mmap as
explained below
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.
AFAIU the i_mutex locking was added to hugetlbfs_read() as per
http://lkml.indiana.edu/hypermail/linux/kernel/0707.2/3066.html to take
care of the race between truncate and read. This patch fixes this by
looking at page->mapping under lock_page() (find_lock_page()) to ensure
that the inode didn't get truncated in the range during a parallel read.
Ideally we can extend the patch to make sure we don't increase i_size in
mmap. But that will break userspace, because applications will now have
to use truncate(2) to increase i_size in hugetlbfs.
Based on the original patch from Hillf Danton.
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Cc: Hillf Danton <dhillf@gmail.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Hugh Dickins <hughd@google.com>
Cc: <stable@kernel.org> [everything after 2007 :)]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/filemap.c')
0 files changed, 0 insertions, 0 deletions