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c967590457
We can concurrently try to open the same sub-channel from 2 paths: path #1: vmbus_onoffer() -> vmbus_process_offer() -> handle_sc_creation(). path #2: storvsc_probe() -> storvsc_connect_to_vsp() -> -> storvsc_channel_init() -> handle_multichannel_storage() -> -> vmbus_are_subchannels_present() -> handle_sc_creation(). They conflict with each other, but it was not an issue before the recent commitae6935ed7d("vmbus: split ring buffer allocation from open"), because at the beginning of vmbus_open() we checked newchannel->state so only one path could succeed, and the other would return with -EINVAL. Afterae6935ed7d, the failing path frees the channel's ringbuffer by vmbus_free_ring(), and this causes a panic later. Commitae6935ed7ditself is good, and it just reveals the longstanding race. We can resolve the issue by removing path #2, i.e. removing the second vmbus_are_subchannels_present() in handle_multichannel_storage(). BTW, the comment "Check to see if sub-channels have already been created" in handle_multichannel_storage() is incorrect: when we unload the driver, we first close the sub-channel(s) and then close the primary channel, next the host sends rescind-offer message(s) so primary->sc_list will become empty. This means the first vmbus_are_subchannels_present() in handle_multichannel_storage() is never useful. Fixes:ae6935ed7d("vmbus: split ring buffer allocation from open") Cc: stable@vger.kernel.org Cc: Long Li <longli@microsoft.com> Cc: Stephen Hemminger <sthemmin@microsoft.com> Cc: K. Y. Srinivasan <kys@microsoft.com> Cc: Haiyang Zhang <haiyangz@microsoft.com> Signed-off-by: Dexuan Cui <decui@microsoft.com> Signed-off-by: K. Y. Srinivasan <kys@microsoft.com> Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.