[PATCH 1/2] vhost/scsi: Improve a size determination in four functions

[PATCH 1/2] vhost/scsi: Improve a size determination in four functions

[SF Markus Elfring]

From: Markus Elfring <elfring@users.sourceforge.net>
Date: Sat, 20 May 2017 13:48:44 +0200

Replace the specification of four data structures by pointer dereferences
as the parameter for the operator "sizeof" to make the corresponding size
determination a bit safer according to the Linux coding style convention.

Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
---
 drivers/vhost/scsi.c | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/drivers/vhost/scsi.c b/drivers/vhost/scsi.c
index fd6c8b66f06f..650533916c19 100644
--- a/drivers/vhost/scsi.c
+++ b/drivers/vhost/scsi.c
@@ -597,8 +597,7 @@ vhost_scsi_get_tag(struct vhost_virtqueue *vq, struct vhost_scsi_tpg *tpg,
 	sg = cmd->tvc_sgl;
 	prot_sg = cmd->tvc_prot_sgl;
 	pages = cmd->tvc_upages;
-	memset(cmd, 0, sizeof(struct vhost_scsi_cmd));
-
+	memset(cmd, 0, sizeof(*cmd));
 	cmd->tvc_sgl = sg;
 	cmd->tvc_prot_sgl = prot_sg;
 	cmd->tvc_upages = pages;
@@ -1757,5 +1756,5 @@ static int vhost_scsi_make_nexus(struct vhost_scsi_tpg *tpg,
 		return -EEXIST;
 	}
 
-	tv_nexus = kzalloc(sizeof(struct vhost_scsi_nexus), GFP_KERNEL);
+	tv_nexus = kzalloc(sizeof(*tv_nexus), GFP_KERNEL);
 	if (!tv_nexus) {
@@ -1958,5 +1957,5 @@ vhost_scsi_make_tpg(struct se_wwn *wwn,
 	if (kstrtou16(name + 5, 10, &tpgt) || tpgt >= VHOST_SCSI_MAX_TARGET)
 		return ERR_PTR(-EINVAL);
 
-	tpg = kzalloc(sizeof(struct vhost_scsi_tpg), GFP_KERNEL);
+	tpg = kzalloc(sizeof(*tpg), GFP_KERNEL);
 	if (!tpg) {
@@ -2012,5 +2011,5 @@ vhost_scsi_make_tport(struct target_fabric_configfs *tf,
 	/* if (vhost_scsi_parse_wwn(name, &wwpn, 1) < 0)
 		return ERR_PTR(-EINVAL); */
 
-	tport = kzalloc(sizeof(struct vhost_scsi_tport), GFP_KERNEL);
+	tport = kzalloc(sizeof(*tport), GFP_KERNEL);
 	if (!tport) {
-- 
2.13.0

[PATCH 2/2] vhost/scsi: Delete error messages for failed memory allocations in five functions

[SF Markus Elfring]

From: Markus Elfring <elfring@users.sourceforge.net>
Date: Sat, 20 May 2017 15:50:30 +0200

Omit seven extra messages for memory allocation failures in these functions.

This issue was detected by using the Coccinelle software.

Link: http://events.linuxfoundation.org/sites/events/files/slides/LCJ16-Refactor_Strings-WSang_0.pdf
Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
---
 drivers/vhost/scsi.c | 24 +++++++-----------------
 1 file changed, 7 insertions(+), 17 deletions(-)

diff --git a/drivers/vhost/scsi.c b/drivers/vhost/scsi.c
index 650533916c19..49d07950e2e5 100644
--- a/drivers/vhost/scsi.c
+++ b/drivers/vhost/scsi.c
@@ -417,5 +417,4 @@ vhost_scsi_allocate_evt(struct vhost_scsi *vs,
 	if (!evt) {
-		vq_err(vq, "Failed to allocate vhost_scsi_evt\n");
 		vs->vs_events_missed = true;
 		return NULL;
 	}
@@ -1722,21 +1721,15 @@ static int vhost_scsi_nexus_cb(struct se_portal_group *se_tpg,
-		if (!tv_cmd->tvc_sgl) {
-			pr_err("Unable to allocate tv_cmd->tvc_sgl\n");
+		if (!tv_cmd->tvc_sgl)
 			goto out;
-		}
 
 		tv_cmd->tvc_upages = kzalloc(sizeof(struct page *) *
 				VHOST_SCSI_PREALLOC_UPAGES, GFP_KERNEL);
-		if (!tv_cmd->tvc_upages) {
-			pr_err("Unable to allocate tv_cmd->tvc_upages\n");
+		if (!tv_cmd->tvc_upages)
 			goto out;
-		}
 
 		tv_cmd->tvc_prot_sgl = kzalloc(sizeof(struct scatterlist) *
 				VHOST_SCSI_PREALLOC_PROT_SGLS, GFP_KERNEL);
-		if (!tv_cmd->tvc_prot_sgl) {
-			pr_err("Unable to allocate tv_cmd->tvc_prot_sgl\n");
+		if (!tv_cmd->tvc_prot_sgl)
 			goto out;
-		}
 	}
 	return 0;
 out:
@@ -1760,6 +1753,5 @@ static int vhost_scsi_make_nexus(struct vhost_scsi_tpg *tpg,
 	if (!tv_nexus) {
 		mutex_unlock(&tpg->tv_tpg_mutex);
-		pr_err("Unable to allocate struct vhost_scsi_nexus\n");
 		return -ENOMEM;
 	}
 	/*
@@ -1961,7 +1953,6 @@ vhost_scsi_make_tpg(struct se_wwn *wwn,
-	if (!tpg) {
-		pr_err("Unable to allocate struct vhost_scsi_tpg");
+	if (!tpg)
 		return ERR_PTR(-ENOMEM);
-	}
+
 	mutex_init(&tpg->tv_tpg_mutex);
 	INIT_LIST_HEAD(&tpg->tv_tpg_list);
 	tpg->tport = tport;
@@ -2015,7 +2006,6 @@ vhost_scsi_make_tport(struct target_fabric_configfs *tf,
-	if (!tport) {
-		pr_err("Unable to allocate struct vhost_scsi_tport");
+	if (!tport)
 		return ERR_PTR(-ENOMEM);
-	}
+
 	tport->tport_wwpn = wwpn;
 	/*
 	 * Determine the emulated Protocol Identifier and Target Port Name
-- 
2.13.0

Re: [PATCH 1/2] vhost/scsi: Improve a size determination in four functions

[Stefan Hajnoczi]

[-- Attachment #1.1: Type: text/plain, Size: 621 bytes --]

On Sat, May 20, 2017 at 04:31:13PM +0200, SF Markus Elfring wrote:
> From: Markus Elfring <elfring@users.sourceforge.net>
> Date: Sat, 20 May 2017 13:48:44 +0200
> 
> Replace the specification of four data structures by pointer dereferences
> as the parameter for the operator "sizeof" to make the corresponding size
> determination a bit safer according to the Linux coding style convention.
> 
> Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
> ---
>  drivers/vhost/scsi.c | 9 ++++-----
>  1 file changed, 4 insertions(+), 5 deletions(-)

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>

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Re: [PATCH 2/2] vhost/scsi: Delete error messages for failed memory allocations in five functions

[Stefan Hajnoczi]

[-- Attachment #1.1: Type: text/plain, Size: 1437 bytes --]

On Sat, May 20, 2017 at 04:32:17PM +0200, SF Markus Elfring wrote:
> From: Markus Elfring <elfring@users.sourceforge.net>
> Date: Sat, 20 May 2017 15:50:30 +0200
> 
> Omit seven extra messages for memory allocation failures in these functions.
> 
> This issue was detected by using the Coccinelle software.
> 
> Link: http://events.linuxfoundation.org/sites/events/files/slides/LCJ16-Refactor_Strings-WSang_0.pdf

Please include an actual explanation for this change instead of linking
to slides.  Why are you trying to get rid of memory allocation failure
messages?

> Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
> ---
>  drivers/vhost/scsi.c | 24 +++++++-----------------
>  1 file changed, 7 insertions(+), 17 deletions(-)
> 
> diff --git a/drivers/vhost/scsi.c b/drivers/vhost/scsi.c
> index 650533916c19..49d07950e2e5 100644
> --- a/drivers/vhost/scsi.c
> +++ b/drivers/vhost/scsi.c
> @@ -417,5 +417,4 @@ vhost_scsi_allocate_evt(struct vhost_scsi *vs,
>  	if (!evt) {
> -		vq_err(vq, "Failed to allocate vhost_scsi_evt\n");

#define vq_err(vq, fmt, ...) do {                                  \
                pr_debug(pr_fmt(fmt), ##__VA_ARGS__);       \
                if ((vq)->error_ctx)                               \
                                eventfd_signal((vq)->error_ctx, 1);\
        } while (0)

You silently dropped the eventfd_signal() call.  Please explain.

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Re: [PATCH 2/2] vhost/scsi: Delete error messages for failed memory allocations in five functions

[SF Markus Elfring]

>> Link: http://events.linuxfoundation.org/sites/events/files/slides/LCJ16-Refactor_Strings-WSang_0.pdf
> 
> Please include an actual explanation for this change instead of linking
> to slides.

Do you care for a bit of code size reduction by removal of questionable
error messages?


> Why are you trying to get rid of memory allocation failure messages?

Do you find information from a Linux allocation failure report sufficient
for any function implementations here?


>> +++ b/drivers/vhost/scsi.c
>> @@ -417,5 +417,4 @@ vhost_scsi_allocate_evt(struct vhost_scsi *vs,
>>  	if (!evt) {
>> -		vq_err(vq, "Failed to allocate vhost_scsi_evt\n");
> 
> #define vq_err(vq, fmt, ...) do {                                  \
>                 pr_debug(pr_fmt(fmt), ##__VA_ARGS__);       \
>                 if ((vq)->error_ctx)                               \
>                                 eventfd_signal((vq)->error_ctx, 1);\
>         } while (0)
> 
> You silently dropped the eventfd_signal() call.

Do you prefer to preserve this special error handling then?

Regards,
Markus

Re: [PATCH 2/2] vhost/scsi: Delete error messages for failed memory allocations in five functions

[Stefan Hajnoczi]

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On Mon, May 22, 2017 at 12:50:39PM +0200, SF Markus Elfring wrote:
> > Why are you trying to get rid of memory allocation failure messages?
> 
> Do you find information from a Linux allocation failure report sufficient
> for any function implementations here?

If kmalloc() and friends guarantee to print a warning and backtrace on
every allocation failure, then there's no need for error messages in
callers.

That seems like good justification that can go in the commit
description, but I'm not sure if kmalloc() and friends guarantee to show
a message (not just the first time, but for every failed allocation)?

> >> +++ b/drivers/vhost/scsi.c
> >> @@ -417,5 +417,4 @@ vhost_scsi_allocate_evt(struct vhost_scsi *vs,
> >>  	if (!evt) {
> >> -		vq_err(vq, "Failed to allocate vhost_scsi_evt\n");
> > 
> > #define vq_err(vq, fmt, ...) do {                                  \
> >                 pr_debug(pr_fmt(fmt), ##__VA_ARGS__);       \
> >                 if ((vq)->error_ctx)                               \
> >                                 eventfd_signal((vq)->error_ctx, 1);\
> >         } while (0)
> > 
> > You silently dropped the eventfd_signal() call.
> 
> Do you prefer to preserve this special error handling then?

Yes, please leave vq_err() calls.

Stefan

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Re: vhost/scsi: Delete error messages for failed memory allocations in five functions

[SF Markus Elfring]

>> Do you find information from a Linux allocation failure report sufficient
>> for any function implementations here?
> 
> If kmalloc() and friends guarantee to print a warning and backtrace on
> every allocation failure, then there's no need for error messages in
> callers.
> 
> That seems like good justification that can go in the commit
> description, but I'm not sure if kmalloc() and friends guarantee to show
> a message (not just the first time, but for every failed allocation)?

I am also looking for a more complete and easier accessible documentation
for this aspect of the desired exception handling.
How would we like to resolve any remaining open issues there?

Regards,
Markus

Re: [PATCH 2/2] vhost/scsi: Delete error messages for failed memory allocations in five functions

[Dan Carpenter]

On Mon, May 22, 2017 at 12:23:20PM +0100, Stefan Hajnoczi wrote:
> I'm not sure if kmalloc() and friends guarantee to show
> a message (not just the first time, but for every failed allocation)?
>

It prints multiple times, but it's ratelimited.  It can also be disabled
using a config option.

See slab_out_of_memory().

regards,
dan carpenter

Re: [PATCH 2/2] vhost/scsi: Delete error messages for failed memory allocations in five functions

[Stefan Hajnoczi]

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On Mon, May 22, 2017 at 03:38:33PM +0300, Dan Carpenter wrote:
> On Mon, May 22, 2017 at 12:23:20PM +0100, Stefan Hajnoczi wrote:
> > I'm not sure if kmalloc() and friends guarantee to show
> > a message (not just the first time, but for every failed allocation)?
> >
> 
> It prints multiple times, but it's ratelimited.  It can also be disabled
> using a config option.
> 
> See slab_out_of_memory().

Thanks!

Stefan

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Re: vhost/scsi: Delete error messages for failed memory allocations in five functions

[Stefan Hajnoczi]

[-- Attachment #1.1: Type: text/plain, Size: 861 bytes --]

On Mon, May 22, 2017 at 01:34:34PM +0200, SF Markus Elfring wrote:
> >> Do you find information from a Linux allocation failure report sufficient
> >> for any function implementations here?
> > 
> > If kmalloc() and friends guarantee to print a warning and backtrace on
> > every allocation failure, then there's no need for error messages in
> > callers.
> > 
> > That seems like good justification that can go in the commit
> > description, but I'm not sure if kmalloc() and friends guarantee to show
> > a message (not just the first time, but for every failed allocation)?
> 
> I am also looking for a more complete and easier accessible documentation
> for this aspect of the desired exception handling.
> How would we like to resolve any remaining open issues there?

No objection from me but please make sure to keep vq_err().

Stefan

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Re: vhost/scsi: Delete error messages for failed memory allocations in five functions

[SF Markus Elfring]

> No objection from me but please make sure to keep vq_err().

How long should I wait before I may dare to send another variant for the
discussed update suggestion?

Which commit message would be acceptable then for this update step?

Regards,
Markus