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Howlett" Cc: linux-kernel@vger.kernel.org, patches@lists.linux.dev, maple-tree@lists.infradead.org, Vlastimil Babka Subject: [RFC 07/11] mm/mmap/vma_merge: set mid to NULL if not applicable Date: Fri, 24 Feb 2023 11:00:18 +0100 Message-Id: <20230224100022.11268-8-vbabka@suse.cz> X-Mailer: git-send-email 2.39.2 In-Reply-To: <20230224100022.11268-1-vbabka@suse.cz> References: <20230224100022.11268-1-vbabka@suse.cz> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 5928614000E X-Stat-Signature: qf3k1dje4gdfohs6rm6wwydsq9yqdsxr X-HE-Tag: 1677232843-825511 X-HE-Meta: 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 b2ov4UN/ yEcJieC23hIIIw4L3Yc5y1fddv3jp6MYyTOdUnSpelZsuVjZsznou/ZHIjmOT7I9PsifMCmDXyMpe5IbygXF+fcG3z8A429AH5xOeDzee66CwZjxYtX0aJqpvJcq27SRAcs2ioZz2Me+qSyXpodOQ/t3WrNUGyXFQtFQsdb6WB4DbgdMbgw2IVgw9oAUGNrUjAI6HcE/R8jLmRlxZVQwqZgihlshak2gQnhv0VV6cYCLe6DH+irW8Wcr2cw== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: There are several places where we test if 'mid' is really the area NNNN in the diagram and the tests have two variants and are non-obvious to follow. Instead, set 'mid' to NULL up-front if it's not the NNNN area, and simplify the tests. Also update the description in comment accordingly. Signed-off-by: Vlastimil Babka --- mm/mmap.c | 21 +++++++++++++-------- 1 file changed, 13 insertions(+), 8 deletions(-) diff --git a/mm/mmap.c b/mm/mmap.c index e7d497237f44..e05bbcaf7b61 100644 --- a/mm/mmap.c +++ b/mm/mmap.c @@ -848,10 +848,11 @@ can_vma_merge_after(struct vm_area_struct *vma, unsigned long vm_flags, * * The following mprotect cases have to be considered, where AAAA is * the area passed down from mprotect_fixup, never extending beyond one - * vma, PPPPPP is the prev vma specified, and NNNNNN the next vma after: + * vma, PPPPPP is the prev vma specified, NNNN is a vma that overlaps + * the area AAAA and XXXXXX the next vma after AAAA: * * AAAA AAAA AAAA - * PPPPPPNNNNNN PPPPPPXXXXXX PPPPPPNNNNNN + * PPPPPPXXXXXX PPPPPPXXXXXX PPPPPPNNNNNN * cannot merge might become might become * PPXXXXXXXXXX PPPPPPPPPPNN * mmap, brk or case 4 below case 5 below @@ -879,9 +880,10 @@ can_vma_merge_after(struct vm_area_struct *vma, unsigned long vm_flags, * * In the code below: * PPPP is represented by *prev - * NNNN is represented by *mid (and possibly equal to *next) - * XXXX is represented by *next or not represented at all. - * AAAA is not represented - it will be merged or the function will return NULL + * NNNN is represented by *mid or not represented at all (NULL) + * XXXX is represented by *next or not represented at all (NULL) + * AAAA is not represented - it will be merged and the vma containing the + * area is returned, or the function will return NULL */ struct vm_area_struct *vma_merge(struct vma_iterator *vmi, struct mm_struct *mm, struct vm_area_struct *prev, unsigned long addr, @@ -918,6 +920,9 @@ struct vm_area_struct *vma_merge(struct vma_iterator *vmi, struct mm_struct *mm, else next = mid; + if (mid && end <= mid->vm_start) + mid = NULL; + /* verify some invariant that must be enforced by the caller */ VM_WARN_ON(prev && addr <= prev->vm_start); VM_WARN_ON(mid && end > mid->vm_end); @@ -952,7 +957,7 @@ struct vm_area_struct *vma_merge(struct vma_iterator *vmi, struct mm_struct *mm, remove = next; /* case 1 */ vma_end = next->vm_end; err = dup_anon_vma(prev, next); - if (mid != next) { /* case 6 */ + if (mid) { /* case 6 */ remove = mid; remove2 = next; if (!next->anon_vma) @@ -960,7 +965,7 @@ struct vm_area_struct *vma_merge(struct vma_iterator *vmi, struct mm_struct *mm, } } else if (merge_prev) { err = 0; /* case 2 */ - if (mid && end > mid->vm_start) { + if (mid) { err = dup_anon_vma(prev, mid); if (end == mid->vm_end) { /* case 7 */ remove = mid; @@ -982,7 +987,7 @@ struct vm_area_struct *vma_merge(struct vma_iterator *vmi, struct mm_struct *mm, vma_end = next->vm_end; vma_pgoff = next->vm_pgoff; err = 0; - if (mid != next) { /* case 8 */ + if (mid) { /* case 8 */ vma_pgoff = mid->vm_pgoff; remove = mid; err = dup_anon_vma(next, mid); -- 2.39.2