Last year, the code that manages GSI channel transactions switched from using spinlock-protected linked lists to using indexes into the ring buffer used for a channel. Recently, Google reported seeing transaction reference count underflows occasionally during shutdown.
Doug Anderson found a way to reproduce the issue reliably, and bisected the issue to the commit that eliminated the linked lists and the lock. The root cause was ultimately determined to be related to unused transactions being committed as part of the modem shutdown cleanup activity. Unused transactions are not normally expected (except in error cases).
The modem uses some ranges of IPA-resident memory, and whenever it shuts down we zero those ranges. In ipa_filter_reset_table() a transaction is allocated to zero modem filter table entries. If hashing is not supported, hashed table memory should not be zeroed. But currently nothing prevents that, and the result is an unused transaction. Something similar occurs when we zero routing table entries for the modem.
By preventing any attempt to clear hashed tables when hashing is not supported, the reference count underflow is avoided in this case.
Note that there likely remains an issue with properly freeing unused transactions (if they occur due to errors). This patch addresses only the underflows that Google originally reported.
Fixes: d338ae28d8a8 ("net: ipa: kill all other transaction lists") Cc: stable@vger.kernel.org # 6.4.x Tested-by: Douglas Anderson dianders@chromium.org Signed-off-by: Alex Elder elder@linaro.org --- drivers/net/ipa/ipa_table.c | 22 ++++++++++++---------- 1 file changed, 12 insertions(+), 10 deletions(-)
diff --git a/drivers/net/ipa/ipa_table.c b/drivers/net/ipa/ipa_table.c index f0529c31d0b6e..7b637bb8b41c8 100644 --- a/drivers/net/ipa/ipa_table.c +++ b/drivers/net/ipa/ipa_table.c @@ -273,16 +273,15 @@ static int ipa_filter_reset(struct ipa *ipa, bool modem) if (ret) return ret;
- ret = ipa_filter_reset_table(ipa, true, false, modem); - if (ret) - return ret; - ret = ipa_filter_reset_table(ipa, false, true, modem); + if (ret || !ipa_table_hash_support(ipa)) + return ret; + + ret = ipa_filter_reset_table(ipa, true, false, modem); if (ret) return ret; - ret = ipa_filter_reset_table(ipa, true, true, modem);
- return ret; + return ipa_filter_reset_table(ipa, true, true, modem); }
/* The AP routes and modem routes are each contiguous within the @@ -291,12 +290,13 @@ static int ipa_filter_reset(struct ipa *ipa, bool modem) * */ static int ipa_route_reset(struct ipa *ipa, bool modem) { + bool hash_support = ipa_table_hash_support(ipa); u32 modem_route_count = ipa->modem_route_count; struct gsi_trans *trans; u16 first; u16 count;
- trans = ipa_cmd_trans_alloc(ipa, 4); + trans = ipa_cmd_trans_alloc(ipa, hash_support ? 4 : 2); if (!trans) { dev_err(&ipa->pdev->dev, "no transaction for %s route reset\n", @@ -313,10 +313,12 @@ static int ipa_route_reset(struct ipa *ipa, bool modem) }
ipa_table_reset_add(trans, false, false, false, first, count); - ipa_table_reset_add(trans, false, true, false, first, count); - ipa_table_reset_add(trans, false, false, true, first, count); - ipa_table_reset_add(trans, false, true, true, first, count); + + if (hash_support) { + ipa_table_reset_add(trans, false, true, false, first, count); + ipa_table_reset_add(trans, false, true, true, first, count); + }
gsi_trans_commit_wait(trans);