On 1/18/23 01:29, Bart Van Assche wrote:
On 1/17/23 14:03, Martin Wilck wrote:
On Tue, 2023-01-17 at 13:52 -0800, Bart Van Assche wrote:
On 1/17/23 13:48, Martin Wilck wrote:
Yes, that was my suggestion. Just defer the scsi_device_put() call
in
alua_rtpg_queue() in the case where the actual RTPG handler is not
queued. I won't have time for that before next week though.
Do you agree that the call trace shared by Steffen is not sufficient
to
conclude that this change is necessary?
Hmm, I suppose I missed your point... to re-iterate my thinking:
1 alua_queue_rtpg() must take a ref to the sdev before queueing work,
whether or not the caller already has one
2 queue_delayed_work() can fail
3 if queue_delayed_work() fails, alua_queue_rtpg() must drop the ref
it just took
4 BUT (and this is what I guess I missed) this ref can't be the last
one dropped, because the caller of alua_rtpg_queue() must still hold
a reference. And scsi_device_put() only sleeps if the last ref is
dropped. Therefore the issue in Steffen's call stack should
indeed be fixed just by removing the might_sleep(). If all callers
callers of alua_rtpg_queue() must hold an sdev reference (I believe
they do), we can indeed remove the might_sleep() entirely.
Is this correct reasoning, and what you meant previously? If yes, I
agree, and I apologize for not realizing it in the first place.
But I think this is subtle enough to deserve a comment in the code.
Yes, that's what I'm thinking.
How about the patch below?
Thanks,
Bart.
[PATCH] scsi: device_handler: alua: Remove a might_sleep() annotation
The might_sleep() annotation in alua_rtpg_queue() is not correct since the
command completion code may call this function from atomic context.
Calling alua_rtpg_queue() from atomic context in the command completion
path is fine since request submitters must hold an sdev reference until
command execution has completed. This patch fixes the following kernel
warning:
BUG: sleeping function called from invalid context at
drivers/scsi/device_handler/scsi_dh_alua.c:992
Call Trace:
dump_stack_lvl+0xac/0x100
__might_resched+0x284/0x2c8
alua_rtpg_queue+0x3c/0x98 [scsi_dh_alua]
alua_check+0x122/0x250 [scsi_dh_alua]
alua_check_sense+0x172/0x228 [scsi_dh_alua]
scsi_check_sense+0x8a/0x2e0
scsi_decide_disposition+0x286/0x298
scsi_complete+0x6a/0x108
blk_complete_reqs+0x6e/0x88
__do_softirq+0x13e/0x6b8
__irq_exit_rcu+0x14a/0x170
irq_exit_rcu+0x22/0x50
do_ext_irq+0x10a/0x1d0
Reported-by: Steffen Maier <maier@xxxxxxxxxxxxx>
Cc: Steffen Maier <maier@xxxxxxxxxxxxx>
Cc: Martin Wilck <mwilck@xxxxxxxx>
Signed-off-by: Bart Van Assche <bvanassche@xxxxxxx>
---
drivers/scsi/device_handler/scsi_dh_alua.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
diff --git a/drivers/scsi/device_handler/scsi_dh_alua.c
b/drivers/scsi/device_handler/scsi_dh_alua.c
index 55a5073248f8..362fa631f39b 100644
--- a/drivers/scsi/device_handler/scsi_dh_alua.c
+++ b/drivers/scsi/device_handler/scsi_dh_alua.c
@@ -987,6 +987,9 @@ static void alua_rtpg_work(struct work_struct *work)
*
* Returns true if and only if alua_rtpg_work() will be called asynchronously.
* That function is responsible for calling @qdata->fn().
+ *
+ * Context: may be called from atomic context (alua_check()) only if the caller
+ * holds an sdev reference.
*/
static bool alua_rtpg_queue(struct alua_port_group *pg,
struct scsi_device *sdev,
@@ -995,8 +998,6 @@ static bool alua_rtpg_queue(struct alua_port_group *pg,
int start_queue = 0;
unsigned long flags;
- might_sleep();
-
I had removed those two lines yesterday for our CI kernel build.
Tonight's run obviously no longer had any related BUG or WARNING.
I checked all dumps from that run to see if anything stalled and whether it was
related to ALUA, but I think we're good.
Tested-by: Steffen Maier <maier@xxxxxxxxxxxxx>
if (WARN_ON_ONCE(!pg) || scsi_device_get(sdev))
return false;
--
Mit freundlichen Gruessen / Kind regards
Steffen Maier
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