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authorKirill A. Shutemov <kirill@shutemov.name>2020-08-14 17:31:27 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2020-08-14 19:56:57 -0700
commite630bfac79456d3acd22c9286b50e83aafb7a07c (patch)
tree38623b93bac25ca17fa9421e1688c2d751434958
parentb96a3db2f37485e902794f28130f70dc834796a4 (diff)
downloadlinux-stericsson-e630bfac79456d3acd22c9286b50e83aafb7a07c.tar.gz
mm/filemap.c: fix a data race in filemap_fault()
struct file_ra_state ra.mmap_miss could be accessed concurrently during page faults as noticed by KCSAN, BUG: KCSAN: data-race in filemap_fault / filemap_map_pages write to 0xffff9b1700a2c1b4 of 4 bytes by task 3292 on cpu 30: filemap_fault+0x920/0xfc0 do_sync_mmap_readahead at mm/filemap.c:2384 (inlined by) filemap_fault at mm/filemap.c:2486 __xfs_filemap_fault+0x112/0x3e0 [xfs] xfs_filemap_fault+0x74/0x90 [xfs] __do_fault+0x9e/0x220 do_fault+0x4a0/0x920 __handle_mm_fault+0xc69/0xd00 handle_mm_fault+0xfc/0x2f0 do_page_fault+0x263/0x6f9 page_fault+0x34/0x40 read to 0xffff9b1700a2c1b4 of 4 bytes by task 3313 on cpu 32: filemap_map_pages+0xc2e/0xd80 filemap_map_pages at mm/filemap.c:2625 do_fault+0x3da/0x920 __handle_mm_fault+0xc69/0xd00 handle_mm_fault+0xfc/0x2f0 do_page_fault+0x263/0x6f9 page_fault+0x34/0x40 Reported by Kernel Concurrency Sanitizer on: CPU: 32 PID: 3313 Comm: systemd-udevd Tainted: G W L 5.5.0-next-20200210+ #1 Hardware name: HPE ProLiant DL385 Gen10/ProLiant DL385 Gen10, BIOS A40 07/10/2019 ra.mmap_miss is used to contribute the readahead decisions, a data race could be undesirable. Both the read and write is only under non-exclusive mmap_sem, two concurrent writers could even underflow the counter. Fix the underflow by writing to a local variable before committing a final store to ra.mmap_miss given a small inaccuracy of the counter should be acceptable. Signed-off-by: Kirill A. Shutemov <kirill@shutemov.name> Signed-off-by: Qian Cai <cai@lca.pw> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Tested-by: Qian Cai <cai@lca.pw> Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Marco Elver <elver@google.com> Link: http://lkml.kernel.org/r/20200211030134.1847-1-cai@lca.pw Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--mm/filemap.c20
1 files changed, 13 insertions, 7 deletions
diff --git a/mm/filemap.c b/mm/filemap.c
index 653190943aa7..1aaea26556cc 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2468,6 +2468,7 @@ static struct file *do_sync_mmap_readahead(struct vm_fault *vmf)
struct address_space *mapping = file->f_mapping;
struct file *fpin = NULL;
pgoff_t offset = vmf->pgoff;
+ unsigned int mmap_miss;
/* If we don't want any read-ahead, don't bother */
if (vmf->vma->vm_flags & VM_RAND_READ)
@@ -2483,14 +2484,15 @@ static struct file *do_sync_mmap_readahead(struct vm_fault *vmf)
}
/* Avoid banging the cache line if not needed */
- if (ra->mmap_miss < MMAP_LOTSAMISS * 10)
- ra->mmap_miss++;
+ mmap_miss = READ_ONCE(ra->mmap_miss);
+ if (mmap_miss < MMAP_LOTSAMISS * 10)
+ WRITE_ONCE(ra->mmap_miss, ++mmap_miss);
/*
* Do we miss much more than hit in this file? If so,
* stop bothering with read-ahead. It will only hurt.
*/
- if (ra->mmap_miss > MMAP_LOTSAMISS)
+ if (mmap_miss > MMAP_LOTSAMISS)
return fpin;
/*
@@ -2516,13 +2518,15 @@ static struct file *do_async_mmap_readahead(struct vm_fault *vmf,
struct file_ra_state *ra = &file->f_ra;
struct address_space *mapping = file->f_mapping;
struct file *fpin = NULL;
+ unsigned int mmap_miss;
pgoff_t offset = vmf->pgoff;
/* If we don't want any read-ahead, don't bother */
if (vmf->vma->vm_flags & VM_RAND_READ || !ra->ra_pages)
return fpin;
- if (ra->mmap_miss > 0)
- ra->mmap_miss--;
+ mmap_miss = READ_ONCE(ra->mmap_miss);
+ if (mmap_miss)
+ WRITE_ONCE(ra->mmap_miss, --mmap_miss);
if (PageReadahead(page)) {
fpin = maybe_unlock_mmap_for_io(vmf, fpin);
page_cache_async_readahead(mapping, ra, file,
@@ -2688,6 +2692,7 @@ void filemap_map_pages(struct vm_fault *vmf,
unsigned long max_idx;
XA_STATE(xas, &mapping->i_pages, start_pgoff);
struct page *page;
+ unsigned int mmap_miss = READ_ONCE(file->f_ra.mmap_miss);
rcu_read_lock();
xas_for_each(&xas, page, end_pgoff) {
@@ -2724,8 +2729,8 @@ void filemap_map_pages(struct vm_fault *vmf,
if (page->index >= max_idx)
goto unlock;
- if (file->f_ra.mmap_miss > 0)
- file->f_ra.mmap_miss--;
+ if (mmap_miss > 0)
+ mmap_miss--;
vmf->address += (xas.xa_index - last_pgoff) << PAGE_SHIFT;
if (vmf->pte)
@@ -2745,6 +2750,7 @@ next:
break;
}
rcu_read_unlock();
+ WRITE_ONCE(file->f_ra.mmap_miss, mmap_miss);
}
EXPORT_SYMBOL(filemap_map_pages);