From: Ashish Kalra <ashish.kalra@amd.com>
Panic notifiers are invoked with RCU read lock held and when the
SNP panic notifier tries to unregister itself from the panic
notifier callback itself it causes a deadlock as notifier
unregistration does RCU synchronization.
Code flow for SNP panic notifier:
snp_shutdown_on_panic() ->
__sev_firmware_shutdown() ->
__sev_snp_shutdown_locked() ->
atomic_notifier_chain_unregister(.., &snp_panic_notifier)
Fix SNP panic notifier to unregister itself during SNP shutdown
only if panic is not in progress.
Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com>
Fixes: 19860c3274fb ("crypto: ccp - Register SNP panic notifier only if SNP is enabled")
Signed-off-by: Ashish Kalra <ashish.kalra@amd.com>
---
drivers/crypto/ccp/sev-dev.c | 10 ++++++++--
1 file changed, 8 insertions(+), 2 deletions(-)
diff --git a/drivers/crypto/ccp/sev-dev.c b/drivers/crypto/ccp/sev-dev.c
index 8fb94c5f006a..17edc6bf5622 100644
--- a/drivers/crypto/ccp/sev-dev.c
+++ b/drivers/crypto/ccp/sev-dev.c
@@ -1787,8 +1787,14 @@ static int __sev_snp_shutdown_locked(int *error, bool panic)
sev->snp_initialized = false;
dev_dbg(sev->dev, "SEV-SNP firmware shutdown\n");
- atomic_notifier_chain_unregister(&panic_notifier_list,
- &snp_panic_notifier);
+ /*
+ * __sev_snp_shutdown_locked() deadlocks when it tries to unregister
+ * itself during panic as the panic notifier is called with RCU read
+ * lock held and notifier unregistration does RCU synchronization.
+ */
+ if (!panic)
+ atomic_notifier_chain_unregister(&panic_notifier_list,
+ &snp_panic_notifier);
/* Reset TMR size back to default */
sev_es_tmr_size = SEV_TMR_SIZE;
--
2.34.1