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sg: remove ->sg_magic member
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This was introduced more than a decade ago when sg chaining was
added, but we never really caught anything with it. The scatterlist
entry size can be critical, since drivers allocate it, so remove
the magic member. Recently it's been triggering allocation stalls
and failures in NVMe.

Tested-by: Jordan Glover <Golden_Miller83@protonmail.ch>
Acked-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
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Jens Axboe committed Jun 29, 2018
1 parent 49f1c61 commit 9544bc5
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Showing 4 changed files with 0 additions and 45 deletions.
3 changes: 0 additions & 3 deletions drivers/gpu/drm/i915/i915_drv.h
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Original file line number Diff line number Diff line change
Expand Up @@ -2238,9 +2238,6 @@ static inline struct scatterlist *____sg_next(struct scatterlist *sg)
**/
static inline struct scatterlist *__sg_next(struct scatterlist *sg)
{
#ifdef CONFIG_DEBUG_SG
BUG_ON(sg->sg_magic != SG_MAGIC);
#endif
return sg_is_last(sg) ? NULL : ____sg_next(sg);
}

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18 changes: 0 additions & 18 deletions include/linux/scatterlist.h
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Original file line number Diff line number Diff line change
Expand Up @@ -9,9 +9,6 @@
#include <asm/io.h>

struct scatterlist {
#ifdef CONFIG_DEBUG_SG
unsigned long sg_magic;
#endif
unsigned long page_link;
unsigned int offset;
unsigned int length;
Expand Down Expand Up @@ -64,7 +61,6 @@ struct sg_table {
*
*/

#define SG_MAGIC 0x87654321
#define SG_CHAIN 0x01UL
#define SG_END 0x02UL

Expand Down Expand Up @@ -98,7 +94,6 @@ static inline void sg_assign_page(struct scatterlist *sg, struct page *page)
*/
BUG_ON((unsigned long) page & (SG_CHAIN | SG_END));
#ifdef CONFIG_DEBUG_SG
BUG_ON(sg->sg_magic != SG_MAGIC);
BUG_ON(sg_is_chain(sg));
#endif
sg->page_link = page_link | (unsigned long) page;
Expand Down Expand Up @@ -129,7 +124,6 @@ static inline void sg_set_page(struct scatterlist *sg, struct page *page,
static inline struct page *sg_page(struct scatterlist *sg)
{
#ifdef CONFIG_DEBUG_SG
BUG_ON(sg->sg_magic != SG_MAGIC);
BUG_ON(sg_is_chain(sg));
#endif
return (struct page *)((sg)->page_link & ~(SG_CHAIN | SG_END));
Expand Down Expand Up @@ -195,9 +189,6 @@ static inline void sg_chain(struct scatterlist *prv, unsigned int prv_nents,
**/
static inline void sg_mark_end(struct scatterlist *sg)
{
#ifdef CONFIG_DEBUG_SG
BUG_ON(sg->sg_magic != SG_MAGIC);
#endif
/*
* Set termination bit, clear potential chain bit
*/
Expand All @@ -215,9 +206,6 @@ static inline void sg_mark_end(struct scatterlist *sg)
**/
static inline void sg_unmark_end(struct scatterlist *sg)
{
#ifdef CONFIG_DEBUG_SG
BUG_ON(sg->sg_magic != SG_MAGIC);
#endif
sg->page_link &= ~SG_END;
}

Expand Down Expand Up @@ -260,12 +248,6 @@ static inline void *sg_virt(struct scatterlist *sg)
static inline void sg_init_marker(struct scatterlist *sgl,
unsigned int nents)
{
#ifdef CONFIG_DEBUG_SG
unsigned int i;

for (i = 0; i < nents; i++)
sgl[i].sg_magic = SG_MAGIC;
#endif
sg_mark_end(&sgl[nents - 1]);
}

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6 changes: 0 additions & 6 deletions lib/scatterlist.c
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Original file line number Diff line number Diff line change
Expand Up @@ -24,9 +24,6 @@
**/
struct scatterlist *sg_next(struct scatterlist *sg)
{
#ifdef CONFIG_DEBUG_SG
BUG_ON(sg->sg_magic != SG_MAGIC);
#endif
if (sg_is_last(sg))
return NULL;

Expand Down Expand Up @@ -111,10 +108,7 @@ struct scatterlist *sg_last(struct scatterlist *sgl, unsigned int nents)
for_each_sg(sgl, sg, nents, i)
ret = sg;

#ifdef CONFIG_DEBUG_SG
BUG_ON(sgl[0].sg_magic != SG_MAGIC);
BUG_ON(!sg_is_last(ret));
#endif
return ret;
}
EXPORT_SYMBOL(sg_last);
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18 changes: 0 additions & 18 deletions tools/virtio/linux/scatterlist.h
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Original file line number Diff line number Diff line change
Expand Up @@ -36,7 +36,6 @@ static inline void sg_assign_page(struct scatterlist *sg, struct page *page)
*/
BUG_ON((unsigned long) page & 0x03);
#ifdef CONFIG_DEBUG_SG
BUG_ON(sg->sg_magic != SG_MAGIC);
BUG_ON(sg_is_chain(sg));
#endif
sg->page_link = page_link | (unsigned long) page;
Expand Down Expand Up @@ -67,7 +66,6 @@ static inline void sg_set_page(struct scatterlist *sg, struct page *page,
static inline struct page *sg_page(struct scatterlist *sg)
{
#ifdef CONFIG_DEBUG_SG
BUG_ON(sg->sg_magic != SG_MAGIC);
BUG_ON(sg_is_chain(sg));
#endif
return (struct page *)((sg)->page_link & ~0x3);
Expand Down Expand Up @@ -116,9 +114,6 @@ static inline void sg_chain(struct scatterlist *prv, unsigned int prv_nents,
**/
static inline void sg_mark_end(struct scatterlist *sg)
{
#ifdef CONFIG_DEBUG_SG
BUG_ON(sg->sg_magic != SG_MAGIC);
#endif
/*
* Set termination bit, clear potential chain bit
*/
Expand All @@ -136,17 +131,11 @@ static inline void sg_mark_end(struct scatterlist *sg)
**/
static inline void sg_unmark_end(struct scatterlist *sg)
{
#ifdef CONFIG_DEBUG_SG
BUG_ON(sg->sg_magic != SG_MAGIC);
#endif
sg->page_link &= ~0x02;
}

static inline struct scatterlist *sg_next(struct scatterlist *sg)
{
#ifdef CONFIG_DEBUG_SG
BUG_ON(sg->sg_magic != SG_MAGIC);
#endif
if (sg_is_last(sg))
return NULL;

Expand All @@ -160,13 +149,6 @@ static inline struct scatterlist *sg_next(struct scatterlist *sg)
static inline void sg_init_table(struct scatterlist *sgl, unsigned int nents)
{
memset(sgl, 0, sizeof(*sgl) * nents);
#ifdef CONFIG_DEBUG_SG
{
unsigned int i;
for (i = 0; i < nents; i++)
sgl[i].sg_magic = SG_MAGIC;
}
#endif
sg_mark_end(&sgl[nents - 1]);
}

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