From: Alex Elder elder@linaro.org
[ Upstream commit 064c9c32b17ca9b36f95eba32ee790dbbebd9a5f ]
Transactions sit on one of several lists, depending on their state (allocated, pending, complete, or polled). A spinlock protects against concurrent access when transactions are moved between these lists.
Transactions are also reference counted. A newly-allocated transaction has an initial count of 1; a transaction is released in gsi_trans_free() only if its decremented reference count reaches 0. Releasing a transaction includes removing it from the polled (or if unused, allocated) list, so the spinlock is acquired when we release a transaction.
The reference count is used to allow a caller to synchronously wait for a committed transaction to complete. In this case, the waiter takes an extra reference to the transaction *before* committing it (so it won't be freed), and releases its reference (calls gsi_trans_free()) when it is done with it.
Similarly, gsi_channel_update() takes an extra reference to ensure a transaction isn't released before the function is done operating on it. Until the transaction is moved to the completed list (by this function) it won't be freed, so this reference is taken "safely."
But in the quiesce path, we want to wait for the "last" transaction, which we find in the completed or polled list. Transactions on these lists can be freed at any time, so we (try to) prevent that by taking the reference while holding the spinlock.
Currently gsi_trans_free() decrements a transaction's reference count unconditionally, acquiring the lock to remove the transaction from its list *only* when the count reaches 0. This does not protect the quiesce path, which depends on the lock to ensure its extra reference prevents release of the transaction.
Fix this by only dropping the last reference to a transaction in gsi_trans_free() while holding the spinlock.
Fixes: 9dd441e4ed575 ("soc: qcom: ipa: GSI transactions") Reported-by: Stephen Boyd swboyd@chromium.org Signed-off-by: Alex Elder elder@linaro.org Link: https://lore.kernel.org/r/20201114182017.28270-1-elder@linaro.org Signed-off-by: Jakub Kicinski kuba@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/net/ipa/gsi_trans.c | 15 ++++++++++++--- 1 file changed, 12 insertions(+), 3 deletions(-)
--- a/drivers/net/ipa/gsi_trans.c +++ b/drivers/net/ipa/gsi_trans.c @@ -363,22 +363,31 @@ struct gsi_trans *gsi_channel_trans_allo return trans; }
-/* Free a previously-allocated transaction (used only in case of error) */ +/* Free a previously-allocated transaction */ void gsi_trans_free(struct gsi_trans *trans) { + refcount_t *refcount = &trans->refcount; struct gsi_trans_info *trans_info; + bool last;
- if (!refcount_dec_and_test(&trans->refcount)) + /* We must hold the lock to release the last reference */ + if (refcount_dec_not_one(refcount)) return;
trans_info = &trans->gsi->channel[trans->channel_id].trans_info;
spin_lock_bh(&trans_info->spinlock);
- list_del(&trans->links); + /* Reference might have been added before we got the lock */ + last = refcount_dec_and_test(refcount); + if (last) + list_del(&trans->links);
spin_unlock_bh(&trans_info->spinlock);
+ if (!last) + return; + ipa_gsi_trans_release(trans);
/* Releasing the reserved TREs implicitly frees the sgl[] and