linux-stable.git/fs/dcache.c, branch v3.18.78

dentry name snapshots

2017-08-11T16:30:11+00:00

commit 49d31c2f389acfe83417083e1208422b4091cd9e upstream.

take_dentry_name_snapshot() takes a safe snapshot of dentry name;
if the name is a short one, it gets copied into caller-supplied
structure, otherwise an extra reference to external name is grabbed
(those are never modified).  In either case the pointer to stable
string is stored into the same structure.

dentry must be held by the caller of take_dentry_name_snapshot(),
but may be freely dropped afterwards - the snapshot will stay
until destroyed by release_dentry_name_snapshot().

Intended use:
	struct name_snapshot s;

	take_dentry_name_snapshot(&s, dentry);
	...
	access s.name
	...
	release_dentry_name_snapshot(&s);

Replaces fsnotify_oldname_...(), gets used in fsnotify to obtain the name
to pass down with event.

Signed-off-by: Al Viro 
Signed-off-by: Greg Kroah-Hartman

fs/dcache.c: fix spin lockup issue on nlru->lock

2017-07-21T06:12:22+00:00

commit b17c070fb624cf10162cf92ea5e1ec25cd8ac176 upstream.

__list_lru_walk_one() acquires nlru spin lock (nlru->lock) for longer
duration if there are more number of items in the lru list.  As per the
current code, it can hold the spin lock for upto maximum UINT_MAX
entries at a time.  So if there are more number of items in the lru
list, then "BUG: spinlock lockup suspected" is observed in the below
path:

  spin_bug+0x90
  do_raw_spin_lock+0xfc
  _raw_spin_lock+0x28
  list_lru_add+0x28
  dput+0x1c8
  path_put+0x20
  terminate_walk+0x3c
  path_lookupat+0x100
  filename_lookup+0x6c
  user_path_at_empty+0x54
  SyS_faccessat+0xd0
  el0_svc_naked+0x24

This nlru->lock is acquired by another CPU in this path -

  d_lru_shrink_move+0x34
  dentry_lru_isolate_shrink+0x48
  __list_lru_walk_one.isra.10+0x94
  list_lru_walk_node+0x40
  shrink_dcache_sb+0x60
  do_remount_sb+0xbc
  do_emergency_remount+0xb0
  process_one_work+0x228
  worker_thread+0x2e0
  kthread+0xf4
  ret_from_fork+0x10

Fix this lockup by reducing the number of entries to be shrinked from
the lru list to 1024 at once.  Also, add cond_resched() before
processing the lru list again.

Link: http://marc.info/?t=149722864900001&r=1&w=2
Link: http://lkml.kernel.org/r/1498707575-2472-1-git-send-email-stummala@codeaurora.org
Signed-off-by: Sahitya Tummala 
Suggested-by: Jan Kara 
Suggested-by: Vladimir Davydov 
Acked-by: Vladimir Davydov 
Cc: Alexander Polakov 
Cc: Al Viro 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds 
Signed-off-by: Greg Kroah-Hartman

fs/dcache.c: avoid soft-lockup in dput()

2016-08-22T16:23:17+00:00

[ Upstream commit 47be61845c775643f1aa4d2a54343549f943c94c ]

We triggered soft-lockup under stress test which
open/access/write/close one file concurrently on more than
five different CPUs:

WARN: soft lockup - CPU#0 stuck for 11s! [who:30631]
...
[] dput+0x100/0x298
[] terminate_walk+0x4c/0x60
[] path_lookupat+0x5cc/0x7a8
[] filename_lookup+0x38/0xf0
[] user_path_at_empty+0x78/0xd0
[] user_path_at+0x1c/0x28
[] SyS_faccessat+0xb4/0x230

->d_lock trylock may failed many times because of concurrently
operations, and dput() may execute a long time.

Fix this by replacing cpu_relax() with cond_resched().
dput() used to be sleepable, so make it sleepable again
should be safe.

Cc: 
Signed-off-by: Wei Fang 
Signed-off-by: Al Viro 
Signed-off-by: Sasha Levin

dcache: let the dentry count go down to zero without taking d_lock

2016-08-22T16:23:17+00:00

[ Upstream commit 360f54796ed65939093ae373b92ebd5ef3341776 ]

We can be more aggressive about this, if we are clever and careful. This is subtle.

Signed-off-by: Linus Torvalds 
Signed-off-by: Al Viro 
Signed-off-by: Sasha Levin

fix d_walk()/non-delayed __d_free() race

2016-06-20T03:47:45+00:00

[ Upstream commit 3d56c25e3bb0726a5c5e16fc2d9e38f8ed763085 ]

Ascend-to-parent logics in d_walk() depends on all encountered child
dentries not getting freed without an RCU delay.  Unfortunately, in
quite a few cases it is not true, with hard-to-hit oopsable race as
the result.

Fortunately, the fix is simiple; right now the rule is "if it ever
been hashed, freeing must be delayed" and changing it to "if it
ever had a parent, freeing must be delayed" closes that hole and
covers all cases the old rule used to cover.  Moreover, pipes and
sockets remain _not_ covered, so we do not introduce RCU delay in
the cases which are the reason for having that delay conditional
in the first place.

Cc: stable@vger.kernel.org # v3.2+ (and watch out for __d_materialise_dentry())
Signed-off-by: Al Viro 
Signed-off-by: Sasha Levin

overlayfs: Make f_path always point to the overlay and f_inode to the underlay

2015-10-28T02:14:24+00:00

[ Upstream commit 4bacc9c9234c7c8eec44f5ed4e960d9f96fa0f01 ]

Make file->f_path always point to the overlay dentry so that the path in
/proc/pid/fd is correct and to ensure that label-based LSMs have access to the
overlay as well as the underlay (path-based LSMs probably don't need it).

Using my union testsuite to set things up, before the patch I see:

	[root@andromeda union-testsuite]# bash 5 /a/foo107
	[root@andromeda union-testsuite]# stat /mnt/a/foo107
	...
	Device: 23h/35d Inode: 13381       Links: 1
	...
	[root@andromeda union-testsuite]# stat -L /proc/$$/fd/5
	...
	Device: 23h/35d Inode: 13381       Links: 1
	...

After the patch:

	[root@andromeda union-testsuite]# bash 5 /mnt/a/foo107
	[root@andromeda union-testsuite]# stat /mnt/a/foo107
	...
	Device: 23h/35d Inode: 40346       Links: 1
	...
	[root@andromeda union-testsuite]# stat -L /proc/$$/fd/5
	...
	Device: 23h/35d Inode: 40346       Links: 1
	...

Note the change in where /proc/$$/fd/5 points to in the ls command.  It was
pointing to /a/foo107 (which doesn't exist) and now points to /mnt/a/foo107
(which is correct).

The inode accessed, however, is the lower layer.  The union layer is on device
25h/37d and the upper layer on 24h/36d.

Signed-off-by: David Howells 
Signed-off-by: Al Viro 
Signed-off-by: Sasha Levin

dcache: Handle escaped paths in prepend_path

2015-10-28T02:14:17+00:00

[ Upstream commit cde93be45a8a90d8c264c776fab63487b5038a65 ]

A rename can result in a dentry that by walking up d_parent
will never reach it's mnt_root.  For lack of a better term
I call this an escaped path.

prepend_path is called by four different functions __d_path,
d_absolute_path, d_path, and getcwd.

__d_path only wants to see paths are connected to the root it passes
in.  So __d_path needs prepend_path to return an error.

d_absolute_path similarly wants to see paths that are connected to
some root.  Escaped paths are not connected to any mnt_root so
d_absolute_path needs prepend_path to return an error greater
than 1.  So escaped paths will be treated like paths on lazily
unmounted mounts.

getcwd needs to prepend "(unreachable)" so getcwd also needs
prepend_path to return an error.

d_path is the interesting hold out.  d_path just wants to print
something, and does not care about the weird cases.  Which raises
the question what should be printed?

Given that / should result in -ENOENT I
believe it is desirable for escaped paths to be printed as empty
paths.  As there are not really any meaninful path components when
considered from the perspective of a mount tree.

So tweak prepend_path to return an empty path with an new error
code of 3 when it encounters an escaped path.

Signed-off-by: "Eric W. Biederman" 
Signed-off-by: Al Viro 
Signed-off-by: Sasha Levin

freeing unlinked file indefinitely delayed

2015-08-27T17:25:40+00:00

[ Upstream commit 75a6f82a0d10ef8f13cd8fe7212911a0252ab99e ]

	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).

Cc: stable@vger.kernel.org # v2.6.38+; earlier ones need s/kill_it/unhash_it/
Acked-by: J. Bruce Fields 
Signed-off-by: Al Viro 
Signed-off-by: Sasha Levin

vfs: Remove incorrect debugging WARN in prepend_path

2015-07-13T12:50:08+00:00

[ Upstream commit 93e3bce6287e1fb3e60d3324ed08555b5bbafa89 ]

The warning message in prepend_path is unclear and outdated.  It was
added as a warning that the mechanism for generating names of pseudo
files had been removed from prepend_path and d_dname should be used
instead.  Unfortunately the warning reads like a general warning,
making it unclear what to do with it.

Remove the warning.  The transition it was added to warn about is long
over, and I added code several years ago which in rare cases causes
the warning to fire on legitimate code, and the warning is now firing
and scaring people for no good reason.

Cc: stable@vger.kernel.org
Reported-by: Ivan Delalande 
Reported-by: Omar Sandoval 
Fixes: f48cfddc6729e ("vfs: In d_path don't call d_dname on a mount point")
Signed-off-by: "Eric W. Biederman" 
Signed-off-by: Sasha Levin

d_walk() might skip too much

2015-06-09T18:31:43+00:00

[ Upstream commit 2159184ea01e4ae7d15f2017e296d4bc82d5aeb0 ]

when we find that a child has died while we'd been trying to ascend,
we should go into the first live sibling itself, rather than its sibling.

Off-by-one in question had been introduced in "deal with deadlock in
d_walk()" and the fix needs to be backported to all branches this one
has been backported to.

Cc: stable@vger.kernel.org # 3.2 and later
Signed-off-by: Al Viro 
Signed-off-by: Sasha Levin