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As of commit d7402513c935 ("arm64: smp: IPI_CPU_STOP and
IPI_CPU_CRASH_STOP should try for NMI"), if we've got pseudo-NMI
enabled then we'll use it to stop CPUs at panic time. This is nice,
but it does mean that there's a pretty good chance that we'll end up
stopping a CPU while it holds the port lock for the console
UART. Specifically, I see a CPU get stopped while holding the port
lock nearly 100% of the time on my sc7180-trogdor based Chromebook by
enabling the "buddy" hardlockup detector and then doing:
sysctl -w kernel.hardlockup_all_cpu_backtrace=1
sysctl -w kernel.hardlockup_panic=1
echo HARDLOCKUP > /sys/kernel/debug/provoke-crash/DIRECT
UART drivers are _supposed_ to handle this case OK and this is why
UART drivers check "oops_in_progress" and only do a "trylock" in that
case. However, before we enabled pseudo-NMI to stop CPUs it wasn't a
very well-tested situation.
Now that we're testing the situation a lot, it can be seen that the
Qualcomm GENI UART driver is pretty broken. Specifically, when I run
my test case and look at the console output I just see a bunch of
garbled output like:
[ 201.069084] NMI backtrace[ 201.069084] NM[ 201.069087] CPU: 6
PID: 10296 Comm: dnsproxyd Not tainted 6.7.0-06265-gb13e8c0ede12
#1 01112b9f14923cbd0b[ 201.069090] Hardware name: Google Lazor
([ 201.069092] pstate: 80400009 (Nzcv daif +PAN -UAO -TCO -DI[
201.069095] pc : smp_call_function_man[ 201.069099]
That's obviously not so great. This happens because each call to the
console driver exits after the data has been written to the FIFO but
before it's actually been flushed out of the serial port. When we have
multiple calls into the console one after the other then (if we can't
get the lock) each call tells the UART to throw away any data in the
FIFO that hadn't been transferred yet.
I've posted up a patch to change the arm64 core to avoid this
situation most of the time [1] much like x86 seems to do, but even if
that patch lands the GENI driver should still be fixed.
>From testing, it appears that we can just delete the cancel/abort in
the case where we weren't able to get the UART lock and the output
looks good. It makes sense that we'd be able to do this since that
means we'll just call into __qcom_geni_serial_console_write() and
__qcom_geni_serial_console_write() looks much like
qcom_geni_serial_poll_put_char() but with a loop. However, it seems
safest to poll the FIFO and make sure it's empty before our
transfer. This should reliably make sure that we're not
interrupting/clobbering any existing transfers.
As part of this change, we'll also avoid re-setting up a TX at the end
of the console write function if we weren't able to get the lock,
since accessing "port->tx_remaining" without the lock is not
safe. This is only needed to re-start userspace initiated transfers.
[1] https://lore.kernel.org/r/20231207170251.1.Id4817adef610302554b8aa42b090d57270dc119c@changeid
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Link: https://lore.kernel.org/r/20240112150307.2.Idb1553d1d22123c377f31eacb4486432f6c9ac8d@changeid
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Bug: 370629635
Change-Id: I0d8abd6cb1471f96d8be5c51061dbd830bed236e
(cherry picked from commit 9e957a155005b16af057e86c6bcc1197cd70a6af)
Signed-off-by: Praveen Talari <quic_ptalari@quicinc.com>
How do I submit patches to Android Common Kernels
-
BEST: Make all of your changes to upstream Linux. If appropriate, backport to the stable releases. These patches will be merged automatically in the corresponding common kernels. If the patch is already in upstream Linux, post a backport of the patch that conforms to the patch requirements below.
- Do not send patches upstream that contain only symbol exports. To be considered for upstream Linux,
additions of
EXPORT_SYMBOL_GPL()require an in-tree modular driver that uses the symbol -- so include the new driver or changes to an existing driver in the same patchset as the export. - When sending patches upstream, the commit message must contain a clear case for why the patch is needed and beneficial to the community. Enabling out-of-tree drivers or functionality is not not a persuasive case.
- Do not send patches upstream that contain only symbol exports. To be considered for upstream Linux,
additions of
-
LESS GOOD: Develop your patches out-of-tree (from an upstream Linux point-of-view). Unless these are fixing an Android-specific bug, these are very unlikely to be accepted unless they have been coordinated with kernel-team@android.com. If you want to proceed, post a patch that conforms to the patch requirements below.
Common Kernel patch requirements
- All patches must conform to the Linux kernel coding standards and pass
scripts/checkpatch.pl - Patches shall not break gki_defconfig or allmodconfig builds for arm, arm64, x86, x86_64 architectures (see https://source.android.com/setup/build/building-kernels)
- If the patch is not merged from an upstream branch, the subject must be tagged with the type of patch:
UPSTREAM:,BACKPORT:,FROMGIT:,FROMLIST:, orANDROID:. - All patches must have a
Change-Id:tag (see https://gerrit-review.googlesource.com/Documentation/user-changeid.html) - If an Android bug has been assigned, there must be a
Bug:tag. - All patches must have a
Signed-off-by:tag by the author and the submitter
Additional requirements are listed below based on patch type
Requirements for backports from mainline Linux: UPSTREAM:, BACKPORT:
- If the patch is a cherry-pick from Linux mainline with no changes at all
- tag the patch subject with
UPSTREAM:. - add upstream commit information with a
(cherry picked from commit ...)line - Example:
- if the upstream commit message is
- tag the patch subject with
important patch from upstream
This is the detailed description of the important patch
Signed-off-by: Fred Jones <fred.jones@foo.org>
- then Joe Smith would upload the patch for the common kernel as
UPSTREAM: important patch from upstream
This is the detailed description of the important patch
Signed-off-by: Fred Jones <fred.jones@foo.org>
Bug: 135791357
Change-Id: I4caaaa566ea080fa148c5e768bb1a0b6f7201c01
(cherry picked from commit c31e73121f4c1ec41143423ac6ce3ce6dafdcec1)
Signed-off-by: Joe Smith <joe.smith@foo.org>
- If the patch requires any changes from the upstream version, tag the patch with
BACKPORT:instead ofUPSTREAM:.- use the same tags as
UPSTREAM: - add comments about the changes under the
(cherry picked from commit ...)line - Example:
- use the same tags as
BACKPORT: important patch from upstream
This is the detailed description of the important patch
Signed-off-by: Fred Jones <fred.jones@foo.org>
Bug: 135791357
Change-Id: I4caaaa566ea080fa148c5e768bb1a0b6f7201c01
(cherry picked from commit c31e73121f4c1ec41143423ac6ce3ce6dafdcec1)
[joe: Resolved minor conflict in drivers/foo/bar.c ]
Signed-off-by: Joe Smith <joe.smith@foo.org>
Requirements for other backports: FROMGIT:, FROMLIST:,
- If the patch has been merged into an upstream maintainer tree, but has not yet
been merged into Linux mainline
- tag the patch subject with
FROMGIT: - add info on where the patch came from as
(cherry picked from commit <sha1> <repo> <branch>). This must be a stable maintainer branch (not rebased, so don't uselinux-nextfor example). - if changes were required, use
BACKPORT: FROMGIT: - Example:
- if the commit message in the maintainer tree is
- tag the patch subject with
important patch from upstream
This is the detailed description of the important patch
Signed-off-by: Fred Jones <fred.jones@foo.org>
- then Joe Smith would upload the patch for the common kernel as
FROMGIT: important patch from upstream
This is the detailed description of the important patch
Signed-off-by: Fred Jones <fred.jones@foo.org>
Bug: 135791357
(cherry picked from commit 878a2fd9de10b03d11d2f622250285c7e63deace
https://git.kernel.org/pub/scm/linux/kernel/git/foo/bar.git test-branch)
Change-Id: I4caaaa566ea080fa148c5e768bb1a0b6f7201c01
Signed-off-by: Joe Smith <joe.smith@foo.org>
- If the patch has been submitted to LKML, but not accepted into any maintainer tree
- tag the patch subject with
FROMLIST: - add a
Link:tag with a link to the submittal on lore.kernel.org - add a
Bug:tag with the Android bug (required for patches not accepted into a maintainer tree) - if changes were required, use
BACKPORT: FROMLIST: - Example:
- tag the patch subject with
FROMLIST: important patch from upstream
This is the detailed description of the important patch
Signed-off-by: Fred Jones <fred.jones@foo.org>
Bug: 135791357
Link: https://lore.kernel.org/lkml/20190619171517.GA17557@someone.com/
Change-Id: I4caaaa566ea080fa148c5e768bb1a0b6f7201c01
Signed-off-by: Joe Smith <joe.smith@foo.org>
Requirements for Android-specific patches: ANDROID:
- If the patch is fixing a bug to Android-specific code
- tag the patch subject with
ANDROID: - add a
Fixes:tag that cites the patch with the bug - Example:
- tag the patch subject with
ANDROID: fix android-specific bug in foobar.c
This is the detailed description of the important fix
Fixes: 1234abcd2468 ("foobar: add cool feature")
Change-Id: I4caaaa566ea080fa148c5e768bb1a0b6f7201c01
Signed-off-by: Joe Smith <joe.smith@foo.org>
- If the patch is a new feature
- tag the patch subject with
ANDROID: - add a
Bug:tag with the Android bug (required for android-specific features)
- tag the patch subject with