Hi All,
With 4.8-rc1 I'm seeing WARN_ON(!host->claimed) triggering in both
mmc_start_request() as well as in mmc_release_host(). The first
indicating that we're executing mmc commands without doing
mmc_claim_host() and the second one indicating that we're
releasing the host without having claimed it first.
The backtraces all point to mmc_blk_issue_rq(). I've done
a very naive hack / workaround:
--- a/drivers/mmc/card/block.c
+++ b/drivers/mmc/card/block.c
@@ -2151,9 +2151,7 @@ static int mmc_blk_issue_rq(struct mmc_queue *mq, struct request *req)
struct mmc_host *host = card->host;
unsigned long flags;
- if (req && !mq->mqrq_prev->req)
- /* claim host only for the first request */
- mmc_get_card(card);
+ mmc_get_card(card);
ret = mmc_blk_part_switch(card, md);
if (ret) {
@@ -2190,15 +2188,8 @@ static int mmc_blk_issue_rq(struct mmc_queue *mq, struct request *req)
}
out:
- if ((!req && !(mq->flags & MMC_QUEUE_NEW_REQUEST)) ||
- mmc_req_is_special(req))
- /*
- * Release host when there are no more requests
- * and after special request(discard, flush) is done.
- * In case sepecial request, there is no reentry to
- * the 'mmc_blk_issue_rq' with 'mqrq_prev->req'.
- */
- mmc_put_card(card);
+ mmc_put_card(card);
+
return ret;
}
Which fixes this, further pointing to the somewhat magical claim / release
code in mmc_blk_issue_rq() being the culprit.
Looking at recent commits these 2 stand out as possible causes of this:
https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=c2df40dfb8c015211ec55f4b1dd0587f875c7b34
https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=3a5e02ced11e22ecd9da3d6710afe15bcfee1d10
I've the feeling that one of these is making mmc_blk_issue_rq() not claiming
the host while it should do so ...
Maybe instead of the magic at the top we need a simple bool to check
if the host is already claimed by the mmc_queue code ?
I can reproduce the WARN_ON's pretty much at will (running 4.8-rc1 on
Allwinner ARM devices with rootfs on a sdcard), let me know if you've
a fix you want me to test.
Regards,
Hans
p.s.
Besides the WARN_ON triggering another side-effect of this is that the
machines will hang at poweroff.
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