Commit76e32a2

vwool

authored and

torvalds

committed

z3fold: fix page locking in z3fold_alloc()

Stress testing of the current z3fold implementation on a 8-core systemrevealed it was possible that a z3fold page deleted from its unbuddiedlist in z3fold_alloc() would be put on another unbuddied list byz3fold_free() while z3fold_alloc() is still processing it. This hasbeen introduced with commit5a27aa8 ("z3fold: add kref refcounting")due to the removal of special handling of a z3fold page not on any listin z3fold_free().To fix this, the z3fold page lock should be taken in z3fold_alloc()before the pool lock is released. To avoid deadlocking, we just try tolock the page as soon as we get a hold of it, and if trylock fails, wedrop this page and take the next one.Signed-off-by: Vitaly Wool <vitalywool@gmail.com>Cc: Dan Streetman <ddstreet@ieee.org>Cc: <Oleksiy.Avramchenko@sony.com>Signed-off-by: Andrew Morton <akpm@linux-foundation.org>Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

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- z3fold.c

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`‎mm/z3fold.c‎`

Lines changed: 7 additions & 2 deletions

Original file line number	Diff line number	Diff line change
`@@ -185,6 +185,12 @@ static inline void z3fold_page_lock(struct z3fold_header *zhdr)`
`185`	`185`	`spin_lock(&zhdr->page_lock);`
`186`	`186`	`}`
`187`	`187`
	`188`	`+/* Try to lock a z3fold page */`
	`189`	`+staticinlineintz3fold_page_trylock(structz3fold_header*zhdr)`
	`190`	`+{`
	`191`	`+returnspin_trylock(&zhdr->page_lock);`
	`192`	`+}`
	`193`	`+`
`188`	`194`	`/* Unlock a z3fold page */`
`189`	`195`	`staticinlinevoidz3fold_page_unlock(structz3fold_header*zhdr)`
`190`	`196`	`{`
`@@ -385,7 +391,7 @@ static int z3fold_alloc(struct z3fold_pool *pool, size_t size, gfp_t gfp,`
`385`	`391`	`spin_lock(&pool->lock);`
`386`	`392`	`zhdr=list_first_entry_or_null(&pool->unbuddied[i],`
`387`	`393`	`structz3fold_header,buddy);`
`388`		`-if (!zhdr) {`
	`394`	`+if (!zhdr\|\| !z3fold_page_trylock(zhdr)) {`
`389`	`395`	`spin_unlock(&pool->lock);`
`390`	`396`	`continue;`
`391`	`397`	`}`
`@@ -394,7 +400,6 @@ static int z3fold_alloc(struct z3fold_pool *pool, size_t size, gfp_t gfp,`
`394`	`400`	`spin_unlock(&pool->lock);`
`395`	`401`
`396`	`402`	`page=virt_to_page(zhdr);`
`397`		`-z3fold_page_lock(zhdr);`
`398`	`403`	`if (zhdr->first_chunks==0) {`
`399`	`404`	`if (zhdr->middle_chunks!=0&&`
`400`	`405`	`chunks >=zhdr->start_middle)`

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Commit76e32a2

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`‎mm/z3fold.c‎`

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