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scsi: zfcp: Clarify & assert the stat_lock locking in zfcp_qdio_send()

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Explain why the plain spin_lock() suffices in current code, even when the
stat_lock is also used by zfcp_qdio_int_req() in tasklet context.

We could also promote the spin_lock() to a spin_lock_irqsave(), but that
would just obfuscate the locking even further.

Link: https://lore.kernel.org/r/b023b1472630f4bf9fce580577d7bb49de89ccbf.1603908167.git.bblock@linux.ibm.com
Reviewed-by: Benjamin Block <bblock@linux.ibm.com>
Reviewed-by: Steffen Maier <maier@linux.ibm.com>
Signed-off-by: Julian Wiedmann <jwi@linux.ibm.com>
Signed-off-by: Benjamin Block <bblock@linux.ibm.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
This commit is contained in:
Julian Wiedmann 2020-10-28 19:30:50 +01:00 committed by Martin K. Petersen
parent 84e7b4169f
commit efd321768d
1 changed files with 8 additions and 0 deletions
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8
drivers/s390/scsi/zfcp_qdio.c
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@ -10,6 +10,7 @@
#define KMSG_COMPONENT "zfcp"
#define pr_fmt(fmt) KMSG_COMPONENT ": " fmt
#include <linux/lockdep.h>
#include <linux/slab.h>
#include <linux/module.h>
#include "zfcp_ext.h"
@ -283,6 +284,13 @@ int zfcp_qdio_send(struct zfcp_qdio *qdio, struct zfcp_qdio_req *q_req)
int retval;
u8 sbal_number = q_req->sbal_number;
/*
* This should actually be a spin_lock_bh(stat_lock), to protect against
* zfcp_qdio_int_req() in tasklet context.
* But we can't do so (and are safe), as we always get called with IRQs
* disabled by spin_lock_irq[save](req_q_lock).
*/
lockdep_assert_irqs_disabled();
spin_lock(&qdio->stat_lock);
zfcp_qdio_account(qdio);
spin_unlock(&qdio->stat_lock);