<feed xmlns='http://www.w3.org/2005/Atom'>
<title>user/sven/linux.git/include/linux, branch v6.12.8</title>
<subtitle>Linux Kernel
</subtitle>
<id>https://git.stealer.net/cgit.cgi/user/sven/linux.git/atom?h=v6.12.8</id>
<link rel='self' href='https://git.stealer.net/cgit.cgi/user/sven/linux.git/atom?h=v6.12.8'/>
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<updated>2025-01-02T09:34:21Z</updated>
<entry>
<title>tracing: Constify string literal data member in struct trace_event_call</title>
<updated>2025-01-02T09:34:21Z</updated>
<author>
<name>Christian Göttsche</name>
<email>cgzones@googlemail.com</email>
</author>
<published>2024-11-25T10:50:25Z</published>
<link rel='alternate' type='text/html' href='https://git.stealer.net/cgit.cgi/user/sven/linux.git/commit/?id=a744146969a0ec8d949aad06889243ad97927a17'/>
<id>urn:sha1:a744146969a0ec8d949aad06889243ad97927a17</id>
<content type='text'>
commit 452f4b31e3f70a52b97890888eeb9eaa9a87139a upstream.

The name member of the struct trace_event_call is assigned with
generated string literals; declare them pointer to read-only.

Reported by clang:

    security/landlock/syscalls.c:179:1: warning: initializing 'char *' with an expression of type 'const char[34]' discards qualifiers [-Wincompatible-pointer-types-discards-qualifiers]
      179 | SYSCALL_DEFINE3(landlock_create_ruleset,
          | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
      180 |                 const struct landlock_ruleset_attr __user *const, attr,
          |                 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
      181 |                 const size_t, size, const __u32, flags)
          |                 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    ./include/linux/syscalls.h:226:36: note: expanded from macro 'SYSCALL_DEFINE3'
      226 | #define SYSCALL_DEFINE3(name, ...) SYSCALL_DEFINEx(3, _##name, __VA_ARGS__)
          |                                    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    ./include/linux/syscalls.h:234:2: note: expanded from macro 'SYSCALL_DEFINEx'
      234 |         SYSCALL_METADATA(sname, x, __VA_ARGS__)                 \
          |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    ./include/linux/syscalls.h:184:2: note: expanded from macro 'SYSCALL_METADATA'
      184 |         SYSCALL_TRACE_ENTER_EVENT(sname);                       \
          |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    ./include/linux/syscalls.h:151:30: note: expanded from macro 'SYSCALL_TRACE_ENTER_EVENT'
      151 |                         .name                   = "sys_enter"#sname,    \
          |                                                   ^~~~~~~~~~~~~~~~~

Cc: stable@vger.kernel.org
Cc: Masami Hiramatsu &lt;mhiramat@kernel.org&gt;
Cc: Mathieu Desnoyers &lt;mathieu.desnoyers@efficios.com&gt;
Cc: Mickaël Salaün &lt;mic@digikod.net&gt;
Cc: Günther Noack &lt;gnoack@google.com&gt;
Cc: Nathan Chancellor &lt;nathan@kernel.org&gt;
Cc: Nick Desaulniers &lt;ndesaulniers@google.com&gt;
Cc: Bill Wendling &lt;morbo@google.com&gt;
Cc: Justin Stitt &lt;justinstitt@google.com&gt;
Link: https://lore.kernel.org/20241125105028.42807-1-cgoettsche@seltendoof.de
Fixes: b77e38aa240c3 ("tracing: add event trace infrastructure")
Signed-off-by: Christian Göttsche &lt;cgzones@googlemail.com&gt;
Signed-off-by: Steven Rostedt (Google) &lt;rostedt@goodmis.org&gt;
Signed-off-by: Greg Kroah-Hartman &lt;gregkh@linuxfoundation.org&gt;
</content>
</entry>
<entry>
<title>freezer, sched: Report frozen tasks as 'D' instead of 'R'</title>
<updated>2025-01-02T09:34:21Z</updated>
<author>
<name>Chen Ridong</name>
<email>chenridong@huawei.com</email>
</author>
<published>2024-12-17T00:48:18Z</published>
<link rel='alternate' type='text/html' href='https://git.stealer.net/cgit.cgi/user/sven/linux.git/commit/?id=79a47fd0f1766064d85c0cea80ca98166087705f'/>
<id>urn:sha1:79a47fd0f1766064d85c0cea80ca98166087705f</id>
<content type='text'>
[ Upstream commit f718faf3940e95d5d34af9041f279f598396ab7d ]

Before commit:

  f5d39b020809 ("freezer,sched: Rewrite core freezer logic")

the frozen task stat was reported as 'D' in cgroup v1.

However, after rewriting the core freezer logic, the frozen task stat is
reported as 'R'. This is confusing, especially when a task with stat of
'S' is frozen.

This bug can be reproduced with these steps:

	$ cd /sys/fs/cgroup/freezer/
	$ mkdir test
	$ sleep 1000 &amp;
	[1] 739         // task whose stat is 'S'
	$ echo 739 &gt; test/cgroup.procs
	$ echo FROZEN &gt; test/freezer.state
	$ ps -aux | grep 739
	root     739  0.1  0.0   8376  1812 pts/0    R    10:56   0:00 sleep 1000

As shown above, a task whose stat is 'S' was changed to 'R' when it was
frozen.

To solve this regression, simply maintain the same reported state as
before the rewrite.

[ mingo: Enhanced the changelog and comments ]

Fixes: f5d39b020809 ("freezer,sched: Rewrite core freezer logic")
Signed-off-by: Chen Ridong &lt;chenridong@huawei.com&gt;
Signed-off-by: Peter Zijlstra (Intel) &lt;peterz@infradead.org&gt;
Signed-off-by: Ingo Molnar &lt;mingo@kernel.org&gt;
Acked-by: Tejun Heo &lt;tj@kernel.org&gt;
Acked-by: Michal Koutný &lt;mkoutny@suse.com&gt;
Link: https://lore.kernel.org/r/20241217004818.3200515-1-chenridong@huaweicloud.com
Signed-off-by: Sasha Levin &lt;sashal@kernel.org&gt;
</content>
</entry>
<entry>
<title>dmaengine: amd: qdma: Remove using the private get and set dma_ops APIs</title>
<updated>2025-01-02T09:34:14Z</updated>
<author>
<name>Lizhi Hou</name>
<email>lizhi.hou@amd.com</email>
</author>
<published>2024-09-18T18:10:22Z</published>
<link rel='alternate' type='text/html' href='https://git.stealer.net/cgit.cgi/user/sven/linux.git/commit/?id=4ecd6f505e4f23689701b4c2b72a1144cd9eee3c'/>
<id>urn:sha1:4ecd6f505e4f23689701b4c2b72a1144cd9eee3c</id>
<content type='text'>
commit dcbef0798eb825cd584f7a93f62bed63f7fbbfc9 upstream.

The get_dma_ops and set_dma_ops APIs were never for driver to use. Remove
these calls from QDMA driver. Instead, pass the DMA device pointer from the
qdma_platdata structure.

Fixes: 73d5fc92a11c ("dmaengine: amd: qdma: Add AMD QDMA driver")
Signed-off-by: Lizhi Hou &lt;lizhi.hou@amd.com&gt;
Reviewed-by: Christoph Hellwig &lt;hch@lst.de&gt;
Link: https://lore.kernel.org/r/20240918181022.2155715-1-lizhi.hou@amd.com
Signed-off-by: Vinod Koul &lt;vkoul@kernel.org&gt;
Signed-off-by: Greg Kroah-Hartman &lt;gregkh@linuxfoundation.org&gt;
</content>
</entry>
<entry>
<title>tcp_bpf: Add sk_rmem_alloc related logic for tcp_bpf ingress redirection</title>
<updated>2025-01-02T09:34:11Z</updated>
<author>
<name>Zijian Zhang</name>
<email>zijianzhang@bytedance.com</email>
</author>
<published>2024-12-10T01:20:39Z</published>
<link rel='alternate' type='text/html' href='https://git.stealer.net/cgit.cgi/user/sven/linux.git/commit/?id=4aa5dcb3891ffca0b09c3dd45328dc2b77194069'/>
<id>urn:sha1:4aa5dcb3891ffca0b09c3dd45328dc2b77194069</id>
<content type='text'>
[ Upstream commit d888b7af7c149c115dd6ac772cc11c375da3e17c ]

When we do sk_psock_verdict_apply-&gt;sk_psock_skb_ingress, an sk_msg will
be created out of the skb, and the rmem accounting of the sk_msg will be
handled by the skb.

For skmsgs in __SK_REDIRECT case of tcp_bpf_send_verdict, when redirecting
to the ingress of a socket, although we sk_rmem_schedule and add sk_msg to
the ingress_msg of sk_redir, we do not update sk_rmem_alloc. As a result,
except for the global memory limit, the rmem of sk_redir is nearly
unlimited. Thus, add sk_rmem_alloc related logic to limit the recv buffer.

Since the function sk_msg_recvmsg and __sk_psock_purge_ingress_msg are
used in these two paths. We use "msg-&gt;skb" to test whether the sk_msg is
skb backed up. If it's not, we shall do the memory accounting explicitly.

Fixes: 604326b41a6f ("bpf, sockmap: convert to generic sk_msg interface")
Signed-off-by: Zijian Zhang &lt;zijianzhang@bytedance.com&gt;
Signed-off-by: Daniel Borkmann &lt;daniel@iogearbox.net&gt;
Reviewed-by: John Fastabend &lt;john.fastabend@gmail.com&gt;
Link: https://lore.kernel.org/bpf/20241210012039.1669389-3-zijianzhang@bytedance.com
Signed-off-by: Sasha Levin &lt;sashal@kernel.org&gt;
</content>
</entry>
<entry>
<title>mm/vmstat: fix a W=1 clang compiler warning</title>
<updated>2025-01-02T09:34:10Z</updated>
<author>
<name>Bart Van Assche</name>
<email>bvanassche@acm.org</email>
</author>
<published>2024-12-12T21:31:26Z</published>
<link rel='alternate' type='text/html' href='https://git.stealer.net/cgit.cgi/user/sven/linux.git/commit/?id=2175b66c7fc0db28e50ba4b1f39119165bb1b655'/>
<id>urn:sha1:2175b66c7fc0db28e50ba4b1f39119165bb1b655</id>
<content type='text'>
[ Upstream commit 30c2de0a267c04046d89e678cc0067a9cfb455df ]

Fix the following clang compiler warning that is reported if the kernel is
built with W=1:

./include/linux/vmstat.h:518:36: error: arithmetic between different enumeration types ('enum node_stat_item' and 'enum lru_list') [-Werror,-Wenum-enum-conversion]
  518 |         return node_stat_name(NR_LRU_BASE + lru) + 3; // skip "nr_"
      |                               ~~~~~~~~~~~ ^ ~~~

Link: https://lkml.kernel.org/r/20241212213126.1269116-1-bvanassche@acm.org
Fixes: 9d7ea9a297e6 ("mm/vmstat: add helpers to get vmstat item names for each enum type")
Signed-off-by: Bart Van Assche &lt;bvanassche@acm.org&gt;
Cc: Konstantin Khlebnikov &lt;koct9i@gmail.com&gt;
Cc: Nathan Chancellor &lt;nathan@kernel.org&gt;
Signed-off-by: Andrew Morton &lt;akpm@linux-foundation.org&gt;
Signed-off-by: Sasha Levin &lt;sashal@kernel.org&gt;
</content>
</entry>
<entry>
<title>epoll: Add synchronous wakeup support for ep_poll_callback</title>
<updated>2024-12-27T13:02:20Z</updated>
<author>
<name>Xuewen Yan</name>
<email>xuewen.yan@unisoc.com</email>
</author>
<published>2024-04-26T08:05:48Z</published>
<link rel='alternate' type='text/html' href='https://git.stealer.net/cgit.cgi/user/sven/linux.git/commit/?id=2d129beb8dd49f12d23f27ecc92cdf544d1e9472'/>
<id>urn:sha1:2d129beb8dd49f12d23f27ecc92cdf544d1e9472</id>
<content type='text'>
commit 900bbaae67e980945dec74d36f8afe0de7556d5a upstream.

Now, the epoll only use wake_up() interface to wake up task.
However, sometimes, there are epoll users which want to use
the synchronous wakeup flag to hint the scheduler, such as
Android binder driver.
So add a wake_up_sync() define, and use the wake_up_sync()
when the sync is true in ep_poll_callback().

Co-developed-by: Jing Xia &lt;jing.xia@unisoc.com&gt;
Signed-off-by: Jing Xia &lt;jing.xia@unisoc.com&gt;
Signed-off-by: Xuewen Yan &lt;xuewen.yan@unisoc.com&gt;
Link: https://lore.kernel.org/r/20240426080548.8203-1-xuewen.yan@unisoc.com
Tested-by: Brian Geffon &lt;bgeffon@google.com&gt;
Reviewed-by: Brian Geffon &lt;bgeffon@google.com&gt;
Reported-by: Benoit Lize &lt;lizeb@google.com&gt;
Signed-off-by: Christian Brauner &lt;brauner@kernel.org&gt;
Cc: Brian Geffon &lt;bgeffon@google.com&gt;
Signed-off-by: Greg Kroah-Hartman &lt;gregkh@linuxfoundation.org&gt;
</content>
</entry>
<entry>
<title>mm: convert partially_mapped set/clear operations to be atomic</title>
<updated>2024-12-27T13:02:20Z</updated>
<author>
<name>Usama Arif</name>
<email>usamaarif642@gmail.com</email>
</author>
<published>2024-12-12T18:33:51Z</published>
<link rel='alternate' type='text/html' href='https://git.stealer.net/cgit.cgi/user/sven/linux.git/commit/?id=a086c8d7f2797c23434baaa4aae0a6bae5dc3414'/>
<id>urn:sha1:a086c8d7f2797c23434baaa4aae0a6bae5dc3414</id>
<content type='text'>
commit 42b2eb69835b0fda797f70eb5b4fc213dbe3a7ea upstream.

Other page flags in the 2nd page, like PG_hwpoison and PG_anon_exclusive
can get modified concurrently.  Changes to other page flags might be lost
if they are happening at the same time as non-atomic partially_mapped
operations.  Hence, make partially_mapped operations atomic.

Link: https://lkml.kernel.org/r/20241212183351.1345389-1-usamaarif642@gmail.com
Fixes: 8422acdc97ed ("mm: introduce a pageflag for partially mapped folios")
Reported-by: David Hildenbrand &lt;david@redhat.com&gt;
Link: https://lore.kernel.org/all/e53b04ad-1827-43a2-a1ab-864c7efecf6e@redhat.com/
Signed-off-by: Usama Arif &lt;usamaarif642@gmail.com&gt;
Acked-by: David Hildenbrand &lt;david@redhat.com&gt;
Acked-by: Johannes Weiner &lt;hannes@cmpxchg.org&gt;
Acked-by: Roman Gushchin &lt;roman.gushchin@linux.dev&gt;
Cc: Barry Song &lt;baohua@kernel.org&gt;
Cc: Domenico Cerasuolo &lt;cerasuolodomenico@gmail.com&gt;
Cc: Jonathan Corbet &lt;corbet@lwn.net&gt;
Cc: Matthew Wilcox &lt;willy@infradead.org&gt;
Cc: Mike Rapoport (Microsoft) &lt;rppt@kernel.org&gt;
Cc: Nico Pache &lt;npache@redhat.com&gt;
Cc: Rik van Riel &lt;riel@surriel.com&gt;
Cc: Ryan Roberts &lt;ryan.roberts@arm.com&gt;
Cc: Shakeel Butt &lt;shakeel.butt@linux.dev&gt;
Cc: Yu Zhao &lt;yuzhao@google.com&gt;
Cc: &lt;stable@vger.kernel.org&gt;
Signed-off-by: Andrew Morton &lt;akpm@linux-foundation.org&gt;
Signed-off-by: Greg Kroah-Hartman &lt;gregkh@linuxfoundation.org&gt;
</content>
</entry>
<entry>
<title>io_uring: Fix registered ring file refcount leak</title>
<updated>2024-12-27T13:02:17Z</updated>
<author>
<name>Jann Horn</name>
<email>jannh@google.com</email>
</author>
<published>2024-12-18T16:56:25Z</published>
<link rel='alternate' type='text/html' href='https://git.stealer.net/cgit.cgi/user/sven/linux.git/commit/?id=06eb0894896bb666f34ea07e73ec00bca865c76a'/>
<id>urn:sha1:06eb0894896bb666f34ea07e73ec00bca865c76a</id>
<content type='text'>
commit 12d908116f7efd34f255a482b9afc729d7a5fb78 upstream.

Currently, io_uring_unreg_ringfd() (which cleans up registered rings) is
only called on exit, but __io_uring_free (which frees the tctx in which the
registered ring pointers are stored) is also called on execve (via
begin_new_exec -&gt; io_uring_task_cancel -&gt; __io_uring_cancel -&gt;
io_uring_cancel_generic -&gt; __io_uring_free).

This means: A process going through execve while having registered rings
will leak references to the rings' `struct file`.

Fix it by zapping registered rings on execve(). This is implemented by
moving the io_uring_unreg_ringfd() from io_uring_files_cancel() into its
callee __io_uring_cancel(), which is called from io_uring_task_cancel() on
execve.

This could probably be exploited *on 32-bit kernels* by leaking 2^32
references to the same ring, because the file refcount is stored in a
pointer-sized field and get_file() doesn't have protection against
refcount overflow, just a WARN_ONCE(); but on 64-bit it should have no
impact beyond a memory leak.

Cc: stable@vger.kernel.org
Fixes: e7a6c00dc77a ("io_uring: add support for registering ring file descriptors")
Signed-off-by: Jann Horn &lt;jannh@google.com&gt;
Link: https://lore.kernel.org/r/20241218-uring-reg-ring-cleanup-v1-1-8f63e999045b@google.com
Signed-off-by: Jens Axboe &lt;axboe@kernel.dk&gt;
Signed-off-by: Greg Kroah-Hartman &lt;gregkh@linuxfoundation.org&gt;
</content>
</entry>
<entry>
<title>tracing: Check "%s" dereference via the field and not the TP_printk format</title>
<updated>2024-12-27T13:02:16Z</updated>
<author>
<name>Steven Rostedt</name>
<email>rostedt@goodmis.org</email>
</author>
<published>2024-12-17T02:41:22Z</published>
<link rel='alternate' type='text/html' href='https://git.stealer.net/cgit.cgi/user/sven/linux.git/commit/?id=d3e73fe7ca21b0c70ffccd756c9b602567ae2cf5'/>
<id>urn:sha1:d3e73fe7ca21b0c70ffccd756c9b602567ae2cf5</id>
<content type='text'>
commit afd2627f727b89496d79a6b934a025fc916d4ded upstream.

The TP_printk() portion of a trace event is executed at the time a event
is read from the trace. This can happen seconds, minutes, hours, days,
months, years possibly later since the event was recorded. If the print
format contains a dereference to a string via "%s", and that string was
allocated, there's a chance that string could be freed before it is read
by the trace file.

To protect against such bugs, there are two functions that verify the
event. The first one is test_event_printk(), which is called when the
event is created. It reads the TP_printk() format as well as its arguments
to make sure nothing may be dereferencing a pointer that was not copied
into the ring buffer along with the event. If it is, it will trigger a
WARN_ON().

For strings that use "%s", it is not so easy. The string may not reside in
the ring buffer but may still be valid. Strings that are static and part
of the kernel proper which will not be freed for the life of the running
system, are safe to dereference. But to know if it is a pointer to a
static string or to something on the heap can not be determined until the
event is triggered.

This brings us to the second function that tests for the bad dereferencing
of strings, trace_check_vprintf(). It would walk through the printf format
looking for "%s", and when it finds it, it would validate that the pointer
is safe to read. If not, it would produces a WARN_ON() as well and write
into the ring buffer "[UNSAFE-MEMORY]".

The problem with this is how it used va_list to have vsnprintf() handle
all the cases that it didn't need to check. Instead of re-implementing
vsnprintf(), it would make a copy of the format up to the %s part, and
call vsnprintf() with the current va_list ap variable, where the ap would
then be ready to point at the string in question.

For architectures that passed va_list by reference this was possible. For
architectures that passed it by copy it was not. A test_can_verify()
function was used to differentiate between the two, and if it wasn't
possible, it would disable it.

Even for architectures where this was feasible, it was a stretch to rely
on such a method that is undocumented, and could cause issues later on
with new optimizations of the compiler.

Instead, the first function test_event_printk() was updated to look at
"%s" as well. If the "%s" argument is a pointer outside the event in the
ring buffer, it would find the field type of the event that is the problem
and mark the structure with a new flag called "needs_test". The event
itself will be marked by TRACE_EVENT_FL_TEST_STR to let it be known that
this event has a field that needs to be verified before the event can be
printed using the printf format.

When the event fields are created from the field type structure, the
fields would copy the field type's "needs_test" value.

Finally, before being printed, a new function ignore_event() is called
which will check if the event has the TEST_STR flag set (if not, it
returns false). If the flag is set, it then iterates through the events
fields looking for the ones that have the "needs_test" flag set.

Then it uses the offset field from the field structure to find the pointer
in the ring buffer event. It runs the tests to make sure that pointer is
safe to print and if not, it triggers the WARN_ON() and also adds to the
trace output that the event in question has an unsafe memory access.

The ignore_event() makes the trace_check_vprintf() obsolete so it is
removed.

Link: https://lore.kernel.org/all/CAHk-=wh3uOnqnZPpR0PeLZZtyWbZLboZ7cHLCKRWsocvs9Y7hQ@mail.gmail.com/

Cc: stable@vger.kernel.org
Cc: Masami Hiramatsu &lt;mhiramat@kernel.org&gt;
Cc: Mark Rutland &lt;mark.rutland@arm.com&gt;
Cc: Mathieu Desnoyers &lt;mathieu.desnoyers@efficios.com&gt;
Cc: Andrew Morton &lt;akpm@linux-foundation.org&gt;
Cc: Al Viro &lt;viro@ZenIV.linux.org.uk&gt;
Cc: Linus Torvalds &lt;torvalds@linux-foundation.org&gt;
Link: https://lore.kernel.org/20241217024720.848621576@goodmis.org
Fixes: 5013f454a352c ("tracing: Add check of trace event print fmts for dereferencing pointers")
Signed-off-by: Steven Rostedt (Google) &lt;rostedt@goodmis.org&gt;
Signed-off-by: Greg Kroah-Hartman &lt;gregkh@linuxfoundation.org&gt;
</content>
</entry>
<entry>
<title>Drivers: hv: util: Avoid accessing a ringbuffer not initialized yet</title>
<updated>2024-12-27T13:02:15Z</updated>
<author>
<name>Michael Kelley</name>
<email>mhklinux@outlook.com</email>
</author>
<published>2024-11-06T15:42:47Z</published>
<link rel='alternate' type='text/html' href='https://git.stealer.net/cgit.cgi/user/sven/linux.git/commit/?id=3dd7a30c6d7f90afcf19e9b072f572ba524d7ec6'/>
<id>urn:sha1:3dd7a30c6d7f90afcf19e9b072f572ba524d7ec6</id>
<content type='text'>
commit 07a756a49f4b4290b49ea46e089cbe6f79ff8d26 upstream.

If the KVP (or VSS) daemon starts before the VMBus channel's ringbuffer is
fully initialized, we can hit the panic below:

hv_utils: Registering HyperV Utility Driver
hv_vmbus: registering driver hv_utils
...
BUG: kernel NULL pointer dereference, address: 0000000000000000
CPU: 44 UID: 0 PID: 2552 Comm: hv_kvp_daemon Tainted: G E 6.11.0-rc3+ #1
RIP: 0010:hv_pkt_iter_first+0x12/0xd0
Call Trace:
...
 vmbus_recvpacket
 hv_kvp_onchannelcallback
 vmbus_on_event
 tasklet_action_common
 tasklet_action
 handle_softirqs
 irq_exit_rcu
 sysvec_hyperv_stimer0
 &lt;/IRQ&gt;
 &lt;TASK&gt;
 asm_sysvec_hyperv_stimer0
...
 kvp_register_done
 hvt_op_read
 vfs_read
 ksys_read
 __x64_sys_read

This can happen because the KVP/VSS channel callback can be invoked
even before the channel is fully opened:
1) as soon as hv_kvp_init() -&gt; hvutil_transport_init() creates
/dev/vmbus/hv_kvp, the kvp daemon can open the device file immediately and
register itself to the driver by writing a message KVP_OP_REGISTER1 to the
file (which is handled by kvp_on_msg() -&gt;kvp_handle_handshake()) and
reading the file for the driver's response, which is handled by
hvt_op_read(), which calls hvt-&gt;on_read(), i.e. kvp_register_done().

2) the problem with kvp_register_done() is that it can cause the
channel callback to be called even before the channel is fully opened,
and when the channel callback is starting to run, util_probe()-&gt;
vmbus_open() may have not initialized the ringbuffer yet, so the
callback can hit the panic of NULL pointer dereference.

To reproduce the panic consistently, we can add a "ssleep(10)" for KVP in
__vmbus_open(), just before the first hv_ringbuffer_init(), and then we
unload and reload the driver hv_utils, and run the daemon manually within
the 10 seconds.

Fix the panic by reordering the steps in util_probe() so the char dev
entry used by the KVP or VSS daemon is not created until after
vmbus_open() has completed. This reordering prevents the race condition
from happening.

Reported-by: Dexuan Cui &lt;decui@microsoft.com&gt;
Fixes: e0fa3e5e7df6 ("Drivers: hv: utils: fix a race on userspace daemons registration")
Cc: stable@vger.kernel.org
Signed-off-by: Michael Kelley &lt;mhklinux@outlook.com&gt;
Acked-by: Wei Liu &lt;wei.liu@kernel.org&gt;
Link: https://lore.kernel.org/r/20241106154247.2271-3-mhklinux@outlook.com
Signed-off-by: Wei Liu &lt;wei.liu@kernel.org&gt;
Message-ID: &lt;20241106154247.2271-3-mhklinux@outlook.com&gt;
Signed-off-by: Greg Kroah-Hartman &lt;gregkh@linuxfoundation.org&gt;
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