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Petersen" , Mike Christie , linux-scsi@vger.kernel.org, target-devel@vger.kernel.org Cc: Bodo Stroesser Subject: [RFC PATCH 6/8] scsi: target: tcmu: Fix and simplify timeout handling Date: Tue, 30 Jun 2020 12:47:07 +0200 Message-Id: <20200630104709.23066-7-bstroesser@ts.fujitsu.com> X-Mailer: git-send-email 2.12.3 In-Reply-To: <20200630104709.23066-1-bstroesser@ts.fujitsu.com> References: <20200630104709.23066-1-bstroesser@ts.fujitsu.com> Sender: target-devel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: target-devel@vger.kernel.org During cmd timeout handling in check_timedout_devices() due to a race it can happen, that tcmu_set_next_deadline() does not start a timer as expected: 1) Either tcmu_check_expired_ring_cmd() checks the inflight_queue or tcmu_check_expired_queue_cmd() checks the qfull_queue while jiffies has the value X 2) At the end of the check the queue contains one remaining command with deadline X (time_after(X, X) is false and thus the command is not handled as being timed out). 3) After tcmu_check_expired_xxxxx_cmd() a timer interrupt happens and jiffies is incremented to X+1. 4) Now tcmu_set_next_deadline() is called, but it skips the command, since time_after(X+1, X) is true. Therefore tcmu_set_next_deadline() finds no new deadline and stops the timer, which it shouldn't. Since commands that time out are removed from inflight_queue or qfull_queue, we don't need the check with time_after() in tcmu_set_next_deadline(), but can use the deadline from the first cmd in the queue. Additionally I replaced the remaining time_after() calls in tcmu_check_expired_xxxxx_cmd() with time_after_eq(), because it is not useful to set the timeout to deadline, but then check for jiffies being greater than deadline. Next I simplified the end of tcmu_handle_completions() and changed the check for no more pending commands from "mb->cmd_tail == mb->cmd_head" to "idr_is_empty(&udev->commands)" because the old check doesn't work correctly if paddings or in the future TMRs are in the ring. Finally tcmu_set_next_deadline() was shifted in the source as preparation for later implementation of tmr_notify callback. Signed-off-by: Bodo Stroesser --- drivers/target/target_core_user.c | 59 +++++++++++++++------------------------ 1 file changed, 23 insertions(+), 36 deletions(-) diff --git a/drivers/target/target_core_user.c b/drivers/target/target_core_user.c index f10d8d182ed9..89f38355a2ab 100644 --- a/drivers/target/target_core_user.c +++ b/drivers/target/target_core_user.c @@ -1129,6 +1129,18 @@ tcmu_queue_cmd(struct se_cmd *se_cmd) return scsi_ret; } +static void tcmu_set_next_deadline(struct list_head *queue, + struct timer_list *timer) +{ + struct tcmu_cmd *cmd; + + if (!list_empty(queue)) { + cmd = list_first_entry(queue, struct tcmu_cmd, queue_entry); + mod_timer(timer, cmd->deadline); + } else + del_timer(timer); +} + static void tcmu_handle_completion(struct tcmu_cmd *cmd, struct tcmu_cmd_entry *entry) { struct se_cmd *se_cmd = cmd->se_cmd; @@ -1196,25 +1208,6 @@ static void tcmu_handle_completion(struct tcmu_cmd *cmd, struct tcmu_cmd_entry * tcmu_free_cmd(cmd); } -static void tcmu_set_next_deadline(struct list_head *queue, - struct timer_list *timer) -{ - struct tcmu_cmd *tcmu_cmd, *tmp_cmd; - unsigned long deadline = 0; - - list_for_each_entry_safe(tcmu_cmd, tmp_cmd, queue, queue_entry) { - if (!time_after(jiffies, tcmu_cmd->deadline)) { - deadline = tcmu_cmd->deadline; - break; - } - } - - if (deadline) - mod_timer(timer, deadline); - else - del_timer(timer); -} - static unsigned int tcmu_handle_completions(struct tcmu_dev *udev) { struct tcmu_mailbox *mb; @@ -1267,22 +1260,16 @@ static unsigned int tcmu_handle_completions(struct tcmu_dev *udev) handled++; } - if (mb->cmd_tail == mb->cmd_head) { - /* no more pending commands */ - del_timer(&udev->cmd_timer); - - if (list_empty(&udev->qfull_queue)) { - /* - * no more pending or waiting commands so try to - * reclaim blocks if needed. - */ - if (atomic_read(&global_db_count) > - tcmu_global_max_blocks) - schedule_delayed_work(&tcmu_unmap_work, 0); - } - } else if (udev->cmd_time_out) { - tcmu_set_next_deadline(&udev->inflight_queue, &udev->cmd_timer); + if (atomic_read(&global_db_count) > tcmu_global_max_blocks && + idr_is_empty(&udev->commands) && list_empty(&udev->qfull_queue)) { + /* + * Allocated blocks exceeded global block limit, currently no + * more pending or waiting commands so try to reclaim blocks. + */ + schedule_delayed_work(&tcmu_unmap_work, 0); } + if (udev->cmd_time_out) + tcmu_set_next_deadline(&udev->inflight_queue, &udev->cmd_timer); return handled; } @@ -1291,7 +1278,7 @@ static void tcmu_check_expired_ring_cmd(struct tcmu_cmd *cmd) { struct se_cmd *se_cmd; - if (!time_after(jiffies, cmd->deadline)) + if (!time_after_eq(jiffies, cmd->deadline)) return; set_bit(TCMU_CMD_BIT_EXPIRED, &cmd->flags); @@ -1310,7 +1297,7 @@ static void tcmu_check_expired_queue_cmd(struct tcmu_cmd *cmd) { struct se_cmd *se_cmd; - if (!time_after(jiffies, cmd->deadline)) + if (!time_after_eq(jiffies, cmd->deadline)) return; pr_debug("Timing out queued cmd %p on dev %s.\n",