On 6/25/24 1:29 AM, Peter Wang (王信友) wrote:
On Mon, 2024-06-24 at 11:01 -0700, Bart Van Assche wrote:
On 6/24/24 5:11 AM, peter.wang@xxxxxxxxxxxx wrote:
diff --git a/drivers/ufs/core/ufs-mcq.c b/drivers/ufs/core/ufs-
mcq.c
index 8944548c30fa..3b2e5bcb08a7 100644
--- a/drivers/ufs/core/ufs-mcq.c
+++ b/drivers/ufs/core/ufs-mcq.c
@@ -512,8 +512,9 @@ int ufshcd_mcq_sq_cleanup(struct ufs_hba *hba,
int task_tag)
return -ETIMEDOUT;
if (task_tag != hba->nutrs - UFSHCD_NUM_RESERVED) {
-if (!cmd)
-return -EINVAL;
+/* Should return 0 if cmd is already complete by irq */
+if (!cmd || !ufshcd_cmd_inflight(cmd))
+return 0;
hwq = ufshcd_mcq_req_to_hwq(hba, scsi_cmd_to_rq(cmd));
} else {
hwq = hba->dev_cmd_queue;
Does the call trace show that blk_mq_unique_tag() tries to
dereference
address 0x194? If so, how is this possible? There are
only two lrbp->cmd assignments in the UFS driver. These assignments
either assign a valid SCSI command pointer or NULL. Even after a SCSI
command has been completed, the SCSI command pointer remains valid.
So
how can an invalid pointer be passed to blk_mq_unique_tag()? Please
root-cause this issue instead of posting a code change that reduces a
race window without closing the race window completely.
blk_mq_unique_tag() tries to dereference address 0x194, and it is null.
Beacuse ISR end this IO by scsi_done, free request will be called and
set mq_hctx null.
The call path is
scsi_done -> scsi_done_internal -> blk_mq_complete_request ->
scsi_complete ->
scsi_finish_command -> scsi_io_completion -> scsi_end_request ->
__blk_mq_end_request ->
blk_mq_free_request -> __blk_mq_free_request
And blk_mq_unique_tag will access mq_hctx then get null pointer error.
Please reference
https://elixir.bootlin.com/linux/latest/source/block/blk-mq.c#L713
https://elixir.bootlin.com/linux/latest/source/block/blk-mq-tag.c#L680
So, the root-casue is very simple, free request then get hwq.
This patch only check if reqesut not free(inflight) then get hwq.
Thought it still have racing winodw, but it is better then do nothing,
right?
Or, maybe we get all cq_lock before get hwq to close the racing window.
But the code may ugly, how do you think?
Please include a full root cause analysis when reposting fixes for the
reported crashes. It is not clear to me how it is possible that an
invalid pointer is passed to blk_mq_unique_tag() (0x194). As I mentioned
in my previous email, freeing a request does not modify the request
pointer and does not modify the SCSI command pointer either. As one can
derive from the blk_mq_alloc_rqs() call stack, memory for struct request
and struct scsi_cmnd is allocated at request queue allocation time and
is not freed until the request queue is freed. Hence, for a given tag,
neither the request pointer nor the SCSI command pointer changes as long
as a request queue exists. Hence my request for an explanation how it is
possible that an invalid pointer was passed to blk_mq_unique_tag().
Thanks,
Bart.
