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From: Luca Coelho <luca@coelho.fi>
To: kvalo@codeaurora.org
Cc: linux-wireless@vger.kernel.org
Subject: [PATCH for v5.11 12/12] iwlwifi: pcie: reschedule in long-running memory reads
Date: Fri, 15 Jan 2021 13:05:58 +0200	[thread overview]
Message-ID: <iwlwifi.20210115130253.217a9d6a6a12.If964cb582ab0aaa94e81c4ff3b279eaafda0fd3f@changeid> (raw)
In-Reply-To: <20210115110558.1248847-1-luca@coelho.fi>

From: Johannes Berg <johannes.berg@intel.com>

If we spin for a long time in memory reads that (for some reason in
hardware) take a long time, then we'll eventually get messages such
as

  watchdog: BUG: soft lockup - CPU#2 stuck for 24s! [kworker/2:2:272]

This is because the reading really does take a very long time, and
we don't schedule, so we're hogging the CPU with this task, at least
if CONFIG_PREEMPT is not set, e.g. with CONFIG_PREEMPT_VOLUNTARY=y.

Previously I misinterpreted the situation and thought that this was
only going to happen if we had interrupts disabled, and then fixed
this (which is good anyway, however), but that didn't always help;
looking at it again now I realized that the spin unlock will only
reschedule if CONFIG_PREEMPT is used.

In order to avoid this issue, change the code to cond_resched() if
we've been spinning for too long here.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Fixes: 04516706bb99 ("iwlwifi: pcie: limit memory read spin time")
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
---
 drivers/net/wireless/intel/iwlwifi/pcie/trans.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/net/wireless/intel/iwlwifi/pcie/trans.c b/drivers/net/wireless/intel/iwlwifi/pcie/trans.c
index e3760c41b31e..ab93a848a466 100644
--- a/drivers/net/wireless/intel/iwlwifi/pcie/trans.c
+++ b/drivers/net/wireless/intel/iwlwifi/pcie/trans.c
@@ -2108,6 +2108,7 @@ static int iwl_trans_pcie_read_mem(struct iwl_trans *trans, u32 addr,
 	while (offs < dwords) {
 		/* limit the time we spin here under lock to 1/2s */
 		unsigned long end = jiffies + HZ / 2;
+		bool resched = false;
 
 		if (iwl_trans_grab_nic_access(trans, &flags)) {
 			iwl_write32(trans, HBUS_TARG_MEM_RADDR,
@@ -2118,10 +2119,15 @@ static int iwl_trans_pcie_read_mem(struct iwl_trans *trans, u32 addr,
 							HBUS_TARG_MEM_RDAT);
 				offs++;
 
-				if (time_after(jiffies, end))
+				if (time_after(jiffies, end)) {
+					resched = true;
 					break;
+				}
 			}
 			iwl_trans_release_nic_access(trans, &flags);
+
+			if (resched)
+				cond_resched();
 		} else {
 			return -EBUSY;
 		}
-- 
2.29.2


      parent reply	other threads:[~2021-01-15 11:33 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-15 11:05 [PATCH for v5.11 00/12] iwlwifi: fixes intended for v5.10 2020-12-02 Luca Coelho
2021-01-15 11:05 ` [PATCH for v5.11 01/12] iwlwifi: mvm: skip power command when unbinding vif during CSA Luca Coelho
2021-01-25 13:54   ` Kalle Valo
2021-01-15 11:05 ` [PATCH for v5.11 02/12] iwlwifi: mvm: take mutex for calling iwl_mvm_get_sync_time() Luca Coelho
2021-01-15 11:05 ` [PATCH for v5.11 03/12] iwlwifi: pcie: avoid potential PNVM leaks Luca Coelho
2021-01-15 11:05 ` [PATCH for v5.11 04/12] iwlwifi: pnvm: don't skip everything when not reloading Luca Coelho
2021-01-15 11:05 ` [PATCH for v5.11 05/12] iwlwifi: pnvm: don't try to load after failures Luca Coelho
2021-01-15 11:05 ` [PATCH for v5.11 06/12] iwlwifi: fix the NMI flow for old devices Luca Coelho
2021-01-15 11:05 ` [PATCH for v5.11 07/12] iwlwifi: queue: don't crash if txq->entries is NULL Luca Coelho
2021-01-15 11:05 ` [PATCH for v5.11 08/12] iwlwifi: pcie: set LTR on more devices Luca Coelho
2021-01-15 11:05 ` [PATCH for v5.11 09/12] iwlwifi: pcie: add a NULL check in iwl_pcie_txq_unmap Luca Coelho
2021-01-15 11:05 ` [PATCH for v5.11 10/12] iwlwifi: pcie: fix context info memory leak Luca Coelho
2021-01-15 11:05 ` [PATCH for v5.11 11/12] iwlwifi: pcie: use jiffies for memory read spin time limit Luca Coelho
2021-01-18 15:16   ` Kalle Valo
2021-01-18 15:18     ` Kalle Valo
2021-01-18 15:51       ` Luca Coelho
2021-01-15 11:05 ` Luca Coelho [this message]

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