Use the XA_TRACK_FREE ability to track which entries have a free bit,
similarly to how it uses the radix tree's IDR_FREE tag. This eliminates
the per-cpu ida_bitmap preload, and fixes the memory consumption
regression I introduced when making the IDR able to store any pointer.
Signed-off-by: Matthew Wilcox <willy@infradead.org>
Introduce xarray value entries and tagged pointers to replace radix
tree exceptional entries. This is a slight change in encoding to allow
the use of an extra bit (we can now store BITS_PER_LONG - 1 bits in a
value entry). It is also a change in emphasis; exceptional entries are
intimidating and different. As the comment explains, you can choose
to store values or pointers in the xarray and they are both first-class
citizens.
Signed-off-by: Matthew Wilcox <willy@infradead.org>
Reviewed-by: Josef Bacik <jbacik@fb.com>
An upcoming change to the encoding of internal entries will set the bottom
two bits to 0b10. Unfortunately, m68k only aligns some data structures
to 2 bytes, so the IDR will interpret them as internal entries and things
will go badly wrong.
Change the radix tree so that it stops either when the node indicates
that it's the bottom of the tree (shift == 0) or when the entry is not an
internal entry. This means we cannot insert an arbitrary kernel pointer
as a multiorder entry, but the IDR does not permit multiorder entries.
Annoyingly, this means the IDR can no longer take advantage of the radix
tree's ability to store a single entry at offset 0 without allocating
memory. A pointer which is 2-byte aligned cannot be stored directly in
the root as it would be indistinguishable from a node, so we must allocate
a node in order to store a 2-byte pointer at index 0. The idr_replace()
function does not take a GFP flags argument, so cannot allocate memory.
If a user inserts a 4-byte aligned pointer at index 0 and then replaces
it with a 2-byte aligned pointer, we must be able to store it.
Arbitrary pointer values are still not permitted; pointers of the
form 2 + (i * 4) for values of i between 0 and 1023 are reserved for
the implementation. These are not valid kernel pointers as they would
point into the zero page.
This change does cause a runtime memory consumption regression for
the IDA. I will recover that later.
Signed-off-by: Matthew Wilcox <willy@infradead.org>
Tested-by: Guenter Roeck <linux@roeck-us.net>
Move these tests from the userspace test-suite to the kernel test-suite.
Also convert check_ida_random to the new API.
Signed-off-by: Matthew Wilcox <willy@infradead.org>
Move as much as possible to kernel space; leave the parts in user space
that rely on checking memory allocation failures to detect the
transition between an exceptional entry and a bitmap.
Signed-off-by: Matthew Wilcox <willy@infradead.org>
Convert to new API and move to kernel space. Take the opportunity to
test the situation a little more thoroughly (ie at different offsets).
Signed-off-by: Matthew Wilcox <willy@infradead.org>
We can't move this test to kernel space because there's no way to
force kmalloc to fail. But we can use the new API and check this
works when the test is in userspace.
Signed-off-by: Matthew Wilcox <willy@infradead.org>
If the radix tree underlying the IDR happens to be full and we attempt
to remove an id which is larger than any id in the IDR, we will call
__radix_tree_delete() with an uninitialised 'slot' pointer, at which
point anything could happen. This was easiest to hit with a single
entry at id 0 and attempting to remove a non-0 id, but it could have
happened with 64 entries and attempting to remove an id >= 64.
Roman said:
The syzcaller test boils down to opening /dev/kvm, creating an
eventfd, and calling a couple of KVM ioctls. None of this requires
superuser. And the result is dereferencing an uninitialized pointer
which is likely a crash. The specific path caught by syzbot is via
KVM_HYPERV_EVENTD ioctl which is new in 4.17. But I guess there are
other user-triggerable paths, so cc:stable is probably justified.
Matthew added:
We have around 250 calls to idr_remove() in the kernel today. Many of
them pass an ID which is embedded in the object they're removing, so
they're safe. Picking a few likely candidates:
drivers/firewire/core-cdev.c looks unsafe; the ID comes from an ioctl.
drivers/gpu/drm/amd/amdgpu/amdgpu_ctx.c is similar
drivers/atm/nicstar.c could be taken down by a handcrafted packet
Link: http://lkml.kernel.org/r/20180518175025.GD6361@bombadil.infradead.org
Fixes: 0a835c4f09 ("Reimplement IDR and IDA using the radix tree")
Reported-by: <syzbot+35666cba7f0a337e2e79@syzkaller.appspotmail.com>
Debugged-by: Roman Kagan <rkagan@virtuozzo.com>
Signed-off-by: Matthew Wilcox <mawilcox@microsoft.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Khalid reported that the kernel selftests are currently failing:
selftests: test_bpf.sh
========================================
test_bpf: [FAIL]
not ok 1..8 selftests: test_bpf.sh [FAIL]
He bisected it to 6ce711f275 ("idr: Make
1-based IDRs more efficient").
The root cause is doing a signed comparison in idr_alloc_u32() instead
of an unsigned comparison. I went looking for any similar problems and
found a couple (which would each result in the failure to warn in two
situations that aren't supposed to happen).
I knocked up a few test-cases to prove that I was right and added them
to the test-suite.
Reported-by: Khalid Aziz <khalid.aziz@oracle.com>
Tested-by: Khalid Aziz <khalid.aziz@oracle.com>
Signed-off-by: Matthew Wilcox <mawilcox@microsoft.com>
About 20% of the IDR users in the kernel want the allocated IDs to start
at 1. The implementation currently searches all the way down the left
hand side of the tree, finds no free ID other than ID 0, walks all the
way back up, and then all the way down again. This patch 'rebases' the
ID so we fill the entire radix tree, rather than leave a gap at 0.
Chris Wilson says: "I did the quick hack of allocating index 0 of the
idr and that eradicated idr_get_free() from being at the top of the
profiles for the many-object stress tests. This improvement will be
much appreciated."
Signed-off-by: Matthew Wilcox <mawilcox@microsoft.com>
It has no more users, so remove it. Move idr_alloc() back into idr.c,
move the guts of idr_alloc_cmn() into idr_alloc_u32(), remove the
wrappers around idr_get_free_cmn() and rename it to idr_get_free().
While there is now no interface to allocate IDs larger than a u32,
the IDR internals remain ready to handle a larger ID should a need arise.
These changes make it possible to provide the guarantee that, if the
nextid pointer points into the object, the object's ID will be initialised
before a concurrent lookup can find the object.
Signed-off-by: Matthew Wilcox <mawilcox@microsoft.com>
One of the charming quirks of the idr_alloc() interface is that you
can pass a negative end and it will be interpreted as "maximum". Ensure
we don't break that.
Signed-off-by: Matthew Wilcox <mawilcox@microsoft.com>
The test was checking the wrong errno; ida_get_new_above() returns
EAGAIN, not ENOMEM on memory allocation failure. Double the number of
threads to increase the chance that we actually exercise this path
during the test suite (it was a bit sporadic before).
Signed-off-by: Matthew Wilcox <mawilcox@microsoft.com>
There's a relatively rare race where we look at the per-cpu preallocated
IDA bitmap, see it's NULL, allocate a new one, and atomically update it.
If the kmalloc() happened to sleep and we were rescheduled to a different
CPU, or an interrupt came in at the exact right time, another task
might have successfully allocated a bitmap and already deposited it.
I forgot what the semantics of cmpxchg() were and ended up freeing the
wrong bitmap leading to KASAN reporting a use-after-free.
Dmitry found the bug with syzkaller & wrote the patch. I wrote the test
case that will reproduce the bug without his patch being applied.
Reported-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Matthew Wilcox <mawilcox@microsoft.com>
Assert that ida_simple_get() allocates an id in the passed range or returns
error on failure, and ida_simple_remove() releases an allocated id.
Signed-off-by: Rehas Sachdeva <aquannie@gmail.com>
Signed-off-by: Matthew Wilcox <mawilcox@microsoft.com>
Assert that idr_get_next() returns the next populated entry in the tree with
an ID greater than or equal to the value pointed to by @nextid argument.
Signed-off-by: Rehas Sachdeva <aquannie@gmail.com>
Signed-off-by: Matthew Wilcox <mawilcox@microsoft.com>
To allow developers to run a subset of tests, build separate multiorder
and idr-test binaries which will run just the tests in those files.
Signed-off-by: Matthew Wilcox <mawilcox@microsoft.com>
Reviewed-by: Rehas Sachdeva <aquannie@gmail.com>
We can use the root entry as a bitmap and save allocating a 128 byte
bitmap for an IDA that contains only a few entries (30 on a 32-bit
machine, 62 on a 64-bit machine). This costs about 300 bytes of kernel
text on x86-64, so as long as 3 IDAs fall into this category, this
is a net win for memory consumption.
Thanks to Rasmus Villemoes for his work documenting the problem and
collecting statistics on IDAs.
Signed-off-by: Matthew Wilcox <mawilcox@microsoft.com>
The IDR is very similar to the radix tree. It has some functionality that
the radix tree did not have (alloc next free, cyclic allocation, a
callback-based for_each, destroy tree), which is readily implementable on
top of the radix tree. A few small changes were needed in order to use a
tag to represent nodes with free space below them. More extensive
changes were needed to support storing NULL as a valid entry in an IDR.
Plain radix trees still interpret NULL as a not-present entry.
The IDA is reimplemented as a client of the newly enhanced radix tree. As
in the current implementation, it uses a bitmap at the last level of the
tree.
Signed-off-by: Matthew Wilcox <willy@infradead.org>
Signed-off-by: Matthew Wilcox <mawilcox@microsoft.com>
Tested-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Konstantin Khlebnikov <koct9i@gmail.com>
Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Matthew Wilcox