Drivers: hv: Always do Hyper-V panic notification in hv_kmsg_dump()

hv_kmsg_dump() currently skips the panic notification entirely if it
doesn't get any message bytes to pass to Hyper-V due to an error from
kmsg_dump_get_buffer(). Skipping the notification is undesirable because
it leaves the Hyper-V host uncertain about the state of a panic'ed guest.

Fix this by always doing the panic notification, even if bytes_written
is zero. Also ensure that bytes_written is initialized, which fixes a
kernel test robot warning. The warning is actually bogus because
kmsg_dump_get_buffer() happens to set bytes_written even if it fails, and
in the kernel test robot's CONFIG_PRINTK not set case, hv_kmsg_dump() is
never called. But do the initialization for robustness and to quiet the
static checker.

Fixes: 9c318a1d9b50 ("Drivers: hv: move panic report code from vmbus to hv early init code")
Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Closes: https://lore.kernel.org/all/202512172103.OcUspn1Z-lkp@intel.com/
Signed-off-by: Michael Kelley <mhklinux@outlook.com>
Reviewed-by: Roman Kisel <vdso@mailbox.org>
Signed-off-by: Wei Liu <wei.liu@kernel.org>

diff --git a/drivers/hv/hv_common.c b/drivers/hv/hv_common.c
index 0a3ab7efed46816b2709458471bead8d8886bfa3..f1c17fb60dc183ddc16b83cf49b916ac253ad53b 100644 (file)
--- a/drivers/hv/hv_common.c
+++ b/drivers/hv/hv_common.c
@@ -195,13 +195,15 @@ static void hv_kmsg_dump(struct kmsg_dumper *dumper,
 
        /*
         * Write dump contents to the page. No need to synchronize; panic should
-        * be single-threaded.
+        * be single-threaded. Ignore failures from kmsg_dump_get_buffer() since
+        * panic notification should be done even if there is no message data.
+        * Don't assume bytes_written is set in case of failure, so initialize it.
         */
        kmsg_dump_rewind(&iter);
-       kmsg_dump_get_buffer(&iter, false, hv_panic_page, HV_HYP_PAGE_SIZE,
+       bytes_written = 0;
+       (void)kmsg_dump_get_buffer(&iter, false, hv_panic_page, HV_HYP_PAGE_SIZE,
                             &bytes_written);
-       if (!bytes_written)
-               return;
+
        /*
         * P3 to contain the physical address of the panic page & P4 to
         * contain the size of the panic data in that page. Rest of the
@@ -210,7 +212,7 @@ static void hv_kmsg_dump(struct kmsg_dumper *dumper,
        hv_set_msr(HV_MSR_CRASH_P0, 0);
        hv_set_msr(HV_MSR_CRASH_P1, 0);
        hv_set_msr(HV_MSR_CRASH_P2, 0);
-       hv_set_msr(HV_MSR_CRASH_P3, virt_to_phys(hv_panic_page));
+       hv_set_msr(HV_MSR_CRASH_P3, bytes_written ? virt_to_phys(hv_panic_page) : 0);
        hv_set_msr(HV_MSR_CRASH_P4, bytes_written);
 
        /*