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  1. 10 Aug, 2015 2 commits
    • Al Viro's avatar
      freeing unlinked file indefinitely delayed · ca3e8840
      Al Viro authored 
      commit 75a6f82a upstream.

	Normally opening a file, unlinking it and then closing will have
the inode freed upon close() (provided that it's not otherwise busy and
has no remaining links, of course).  However, there's one case where that
does *not* happen.  Namely, if you open it by fhandle with cold dcache,
then unlink() and close().

	In normal case you get d_delete() in unlink(2) notice that dentry
is busy and unhash it; on the final dput() it will be forcibly evicted from
dcache, triggering iput() and inode removal.  In this case, though, we end
up with *two* dentries - disconnected (created by open-by-fhandle) and
regular one (used by unlink()).  The latter will have its reference to inode
dropped just fine, but the former will not - it's considered hashed (it
is on the ->s_anon list), so it will stay around until the memory pressure
will finally do it in.  As the result, we have the final iput() delayed
indefinitely.  It's trivial to reproduce -

void flush_dcache(void)
{
        system("mount -o remount,rw /");
}

static char buf[20 * 1024 * 1024];

main()
{
        int fd;
        union {
                struct file_handle f;
                char buf[MAX_HANDLE_SZ];
        } x;
        int m;

        x.f.handle_bytes = sizeof(x);
        chdir("/root");
        mkdir("foo", 0700);
        fd = open("foo/bar", O_CREAT | O_RDWR, 0600);
        close(fd);
        name_to_handle_at(AT_FDCWD, "foo/bar", &x.f, &m, 0);
        flush_dcache();
        fd = open_by_handle_at(AT_FDCWD, &x.f, O_RDWR);
        unlink("foo/bar");
        write(fd, buf, sizeof(buf));
        system("df .");			/* 20Mb eaten */
        close(fd);
        system("df .");			/* should've freed those 20Mb */
        flush_dcache();
        system("df .");			/* should be the same as #2 */
}

will spit out something like
Filesystem     1K-blocks   Used Available Use% Mounted on
/dev/root         322023 303843      1131 100% /
Filesystem     1K-blocks   Used Available Use% Mounted on
/dev/root         322023 303843      1131 100% /
Filesystem     1K-blocks   Used Available Use% Mounted on
/dev/root         322023 283282     21692  93% /
- inode gets freed only when dentry is finally evicted (here we trigger
than by remount; normally it would've happened in response to memory
pressure hell knows when).
Acked-by: default avatarJ. Bruce Fields <bfields@fieldses.org>
Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
      ca3e8840
    • Kirill A. Shutemov's avatar
      mm: avoid setting up anonymous pages into file mapping · 9f7fa1bc
      Kirill A. Shutemov authored 
      commit 6b7339f4 upstream.

Reading page fault handler code I've noticed that under right
circumstances kernel would map anonymous pages into file mappings: if
the VMA doesn't have vm_ops->fault() and the VMA wasn't fully populated
on ->mmap(), kernel would handle page fault to not populated pte with
do_anonymous_page().

Let's change page fault handler to use do_anonymous_page() only on
anonymous VMA (->vm_ops == NULL) and make sure that the VMA is not
shared.

For file mappings without vm_ops->fault() or shred VMA without vm_ops,
page fault on pte_none() entry would lead to SIGBUS.
Signed-off-by: default avatarKirill A. Shutemov <kirill.shutemov@linux.intel.com>
Acked-by: default avatarOleg Nesterov <oleg@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Willy Tarreau <w@1wt.eu>
Cc: stable@vger.kernel.org
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
      9f7fa1bc
  3. 03 Aug, 2015 38 commits
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