mirror of
https://github.com/rd-stuffs/msm-4.14.git
synced 2025-02-20 11:45:48 +08:00
a8dddf8b08
commit 73052b0daee0b750b39af18460dfec683e4f5887 upstream.
d_delete only unhashes an entry if it is reached with
dentry->d_lockref.count != 1. Prior to commit 8ead9dd54716 ("devpts:
more pty driver interface cleanups"), d_delete was called on a dentry
from devpts_pty_kill with two references held, which would trigger the
unhashing, and the subsequent dputs would release it.
Commit 8ead9dd54716 reworked devpts_pty_kill to stop acquiring the second
reference from d_find_alias, and the d_delete call left the dentries
still on the hashed list without actually ever being dropped from dcache
before explicit cleanup. This causes the number of negative dentries for
devpts to pile up, and an `ls /dev/pts` invocation can take seconds to
return.
Provide always_delete_dentry() from simple_dentry_operations
as .d_delete for devpts, to make the dentry be dropped from dcache.
Without this cleanup, the number of dentries in /dev/pts/ can be grown
arbitrarily as:
`python -c 'import pty; pty.spawn(["ls", "/dev/pts"])'`
A systemtap probe on dcache_readdir to count d_subdirs shows this count
to increase with each pty spawn invocation above:
probe kernel.function("dcache_readdir") {
subdirs = &@cast($file->f_path->dentry, "dentry")->d_subdirs;
p = subdirs;
p = @cast(p, "list_head")->next;
i = 0
while (p != subdirs) {
p = @cast(p, "list_head")->next;
i = i+1;
}
printf("number of dentries: %d\n", i);
}
Fixes: 8ead9dd54716 ("devpts: more pty driver interface cleanups")
Signed-off-by: Varad Gautam <vrd@amazon.de>
Reported-by: Zheng Wang <wanz@amazon.de>
Reported-by: Brandon Schwartz <bsschwar@amazon.de>
Root-caused-by: Maximilian Heyne <mheyne@amazon.de>
Root-caused-by: Nicolas Pernas Maradei <npernas@amazon.de>
CC: David Woodhouse <dwmw@amazon.co.uk>
CC: Maximilian Heyne <mheyne@amazon.de>
CC: Stefan Nuernberger <snu@amazon.de>
CC: Amit Shah <aams@amazon.de>
CC: Linus Torvalds <torvalds@linux-foundation.org>
CC: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
CC: Al Viro <viro@ZenIV.linux.org.uk>
CC: Christian Brauner <christian.brauner@ubuntu.com>
CC: Eric W. Biederman <ebiederm@xmission.com>
CC: Matthew Wilcox <willy@infradead.org>
CC: Eric Biggers <ebiggers@google.com>
CC: <stable@vger.kernel.org> # 4.9+
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.