1.. _stable_kernel_rules:
2
3Everything you ever wanted to know about Linux -stable releases
4===============================================================
5
6Rules on what kind of patches are accepted, and which ones are not, into the
7"-stable" tree:
8
9 - It or an equivalent fix must already exist in Linus' tree (upstream).
10 - It must be obviously correct and tested.
11 - It cannot be bigger than 100 lines, with context.
12 - It must follow the
13   :ref:`Documentation/process/submitting-patches.rst <submittingpatches>`
14   rules.
15 - It must either fix a real bug that bothers people or just add a device ID.
16   To elaborate on the former:
17
18   - It fixes a problem like an oops, a hang, data corruption, a real security
19     issue, a hardware quirk, a build error (but not for things marked
20     CONFIG_BROKEN), or some "oh, that's not good" issue.
21   - Serious issues as reported by a user of a distribution kernel may also
22     be considered if they fix a notable performance or interactivity issue.
23     As these fixes are not as obvious and have a higher risk of a subtle
24     regression they should only be submitted by a distribution kernel
25     maintainer and include an addendum linking to a bugzilla entry if it
26     exists and additional information on the user-visible impact.
27   - No "This could be a problem..." type of things like a "theoretical race
28     condition", unless an explanation of how the bug can be exploited is also
29     provided.
30   - No "trivial" fixes without benefit for users (spelling changes, whitespace
31     cleanups, etc).
32
33
34Procedure for submitting patches to the -stable tree
35----------------------------------------------------
36
37.. note::
38
39   Security patches should not be handled (solely) by the -stable review
40   process but should follow the procedures in
41   :ref:`Documentation/process/security-bugs.rst <securitybugs>`.
42
43There are three options to submit a change to -stable trees:
44
45 1. Add a 'stable tag' to the description of a patch you then submit for
46    mainline inclusion.
47 2. Ask the stable team to pick up a patch already mainlined.
48 3. Submit a patch to the stable team that is equivalent to a change already
49    mainlined.
50
51The sections below describe each of the options in more detail.
52
53:ref:`option_1` is **strongly** preferred, it is the easiest and most common.
54:ref:`option_2` is mainly meant for changes where backporting was not considered
55at the time of submission. :ref:`option_3` is an alternative to the two earlier
56options for cases where a mainlined patch needs adjustments to apply in older
57series (for example due to API changes).
58
59When using option 2 or 3 you can ask for your change to be included in specific
60stable series. When doing so, ensure the fix or an equivalent is applicable,
61submitted, or already present in all newer stable trees still supported. This is
62meant to prevent regressions that users might later encounter on updating, if
63e.g. a fix merged for 5.19-rc1 would be backported to 5.10.y, but not to 5.15.y.
64
65.. _option_1:
66
67Option 1
68********
69
70To have a patch you submit for mainline inclusion later automatically picked up
71for stable trees, add the tag
72
73.. code-block:: none
74
75     Cc: stable@vger.kernel.org
76
77in the sign-off area. Once the patch is mainlined it will be applied to the
78stable tree without anything else needing to be done by the author or
79subsystem maintainer.
80
81To sent additional instructions to the stable team, use a shell-style inline
82comment:
83
84 * To specify any additional patch prerequisites for cherry picking use the
85   following format in the sign-off area:
86
87   .. code-block:: none
88
89     Cc: <stable@vger.kernel.org> # 3.3.x: a1f84a3: sched: Check for idle
90     Cc: <stable@vger.kernel.org> # 3.3.x: 1b9508f: sched: Rate-limit newidle
91     Cc: <stable@vger.kernel.org> # 3.3.x: fd21073: sched: Fix affinity logic
92     Cc: <stable@vger.kernel.org> # 3.3.x
93     Signed-off-by: Ingo Molnar <mingo@elte.hu>
94
95   The tag sequence has the meaning of:
96
97   .. code-block:: none
98
99     git cherry-pick a1f84a3
100     git cherry-pick 1b9508f
101     git cherry-pick fd21073
102     git cherry-pick <this commit>
103
104 * For patches that may have kernel version prerequisites specify them using
105   the following format in the sign-off area:
106
107   .. code-block:: none
108
109     Cc: <stable@vger.kernel.org> # 3.3.x
110
111   The tag has the meaning of:
112
113   .. code-block:: none
114
115     git cherry-pick <this commit>
116
117   For each "-stable" tree starting with the specified version.
118
119   Note, such tagging is unnecessary if the stable team can derive the
120   appropriate versions from Fixes: tags.
121
122 * To delay pick up of patches, use the following format:
123
124   .. code-block:: none
125
126     Cc: <stable@vger.kernel.org> # after 4 weeks in mainline
127
128 * For any other requests, just add a note to the stable tag. This for example
129   can be used to point out known problems:
130
131   .. code-block:: none
132
133     Cc: <stable@vger.kernel.org> # see patch description, needs adjustments for <= 6.3
134
135.. _option_2:
136
137Option 2
138********
139
140If the patch already has been merged to mainline, send an email to
141stable@vger.kernel.org containing the subject of the patch, the commit ID,
142why you think it should be applied, and what kernel versions you wish it to
143be applied to.
144
145.. _option_3:
146
147Option 3
148********
149
150Send the patch, after verifying that it follows the above rules, to
151stable@vger.kernel.org and mention the kernel versions you wish it to be applied
152to. When doing so, you must note the upstream commit ID in the changelog of your
153submission with a separate line above the commit text, like this:
154
155.. code-block:: none
156
157    commit <sha1> upstream.
158
159or alternatively:
160
161.. code-block:: none
162
163    [ Upstream commit <sha1> ]
164
165If the submitted patch deviates from the original upstream patch (for example
166because it had to be adjusted for the older API), this must be very clearly
167documented and justified in the patch description.
168
169
170Following the submission
171------------------------
172
173The sender will receive an ACK when the patch has been accepted into the
174queue, or a NAK if the patch is rejected.  This response might take a few
175days, according to the schedules of the stable team members.
176
177If accepted, the patch will be added to the -stable queue, for review by other
178developers and by the relevant subsystem maintainer.
179
180
181Review cycle
182------------
183
184 - When the -stable maintainers decide for a review cycle, the patches will be
185   sent to the review committee, and the maintainer of the affected area of
186   the patch (unless the submitter is the maintainer of the area) and CC: to
187   the linux-kernel mailing list.
188 - The review committee has 48 hours in which to ACK or NAK the patch.
189 - If the patch is rejected by a member of the committee, or linux-kernel
190   members object to the patch, bringing up issues that the maintainers and
191   members did not realize, the patch will be dropped from the queue.
192 - The ACKed patches will be posted again as part of release candidate (-rc)
193   to be tested by developers and testers.
194 - Usually only one -rc release is made, however if there are any outstanding
195   issues, some patches may be modified or dropped or additional patches may
196   be queued. Additional -rc releases are then released and tested until no
197   issues are found.
198 - Responding to the -rc releases can be done on the mailing list by sending
199   a "Tested-by:" email with any testing information desired. The "Tested-by:"
200   tags will be collected and added to the release commit.
201 - At the end of the review cycle, the new -stable release will be released
202   containing all the queued and tested patches.
203 - Security patches will be accepted into the -stable tree directly from the
204   security kernel team, and not go through the normal review cycle.
205   Contact the kernel security team for more details on this procedure.
206
207
208Trees
209-----
210
211 - The queues of patches, for both completed versions and in progress
212   versions can be found at:
213
214	https://git.kernel.org/pub/scm/linux/kernel/git/stable/stable-queue.git
215
216 - The finalized and tagged releases of all stable kernels can be found
217   in separate branches per version at:
218
219	https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
220
221 - The release candidate of all stable kernel versions can be found at:
222
223        https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable-rc.git/
224
225   .. warning::
226      The -stable-rc tree is a snapshot in time of the stable-queue tree and
227      will change frequently, hence will be rebased often. It should only be
228      used for testing purposes (e.g. to be consumed by CI systems).
229
230
231Review committee
232----------------
233
234 - This is made up of a number of kernel developers who have volunteered for
235   this task, and a few that haven't.
236