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shmem: fix quota lock nesting in huge hole handling

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i_pages lock nests inside i_lock, but shmem_charge() and shmem_uncharge()
were being called from THP splitting or collapsing while i_pages lock was
held, and now go on to call dquot_alloc_block_nodirty() which takes
i_lock to update i_blocks.

We may well want to take i_lock out of this path later, in the non-quota
case even if it's left in the quota case (or perhaps use i_lock instead
of shmem's info->lock throughout); but don't get into that at this time.

Move the shmem_charge() and shmem_uncharge() calls out from under i_pages
lock, accounting the full batch of holes in a single call.

Still pass the pages argument to shmem_uncharge(), but it happens now to
be unused: shmem_recalc_inode() is designed to account for clean pages
freed behind shmem's back, so it gets the accounting right by itself;
then the later call to shmem_inode_unacct_blocks() led to imbalance
(that WARN_ON(inode->i_blocks) in shmem_evict_inode()).

Reported-by: syzbot+38ca19393fb3344f57e6@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/lkml/0000000000008e62f40600bfe080@google.com/
Reported-by: syzbot+440ff8cca06ee7a1d4db@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/lkml/00000000000076a7840600bfb6e8@google.com/
Signed-off-by: Hugh Dickins <hughd@google.com>
Tested-by: Carlos Maiolino <cmaiolino@redhat.com>
Reviewed-by: Carlos Maiolino <cmaiolino@redhat.com>
Message-Id: <20230725144510.253763-8-cem@kernel.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>
This commit is contained in:
Hugh Dickins 2023-07-25 16:45:10 +02:00 committed by Christian Brauner
parent de4c0e7ca8
commit 509f006932
3 changed files with 20 additions and 18 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

6
mm/huge_memory.c
View File

@ -2521,7 +2521,7 @@ static void __split_huge_page(struct page *page, struct list_head *list,
struct address_space *swap_cache = NULL;
unsigned long offset = 0;
unsigned int nr = thp_nr_pages(head);
int i;
int i, nr_dropped = 0;
/* complete memcg works before add pages to LRU */
split_page_memcg(head, nr);
@ -2546,7 +2546,7 @@ static void __split_huge_page(struct page *page, struct list_head *list,
struct folio *tail = page_folio(head + i);
if (shmem_mapping(head->mapping))
shmem_uncharge(head->mapping->host, 1);
nr_dropped++;
else if (folio_test_clear_dirty(tail))
folio_account_cleaned(tail,
inode_to_wb(folio->mapping->host));
@ -2583,6 +2583,8 @@ static void __split_huge_page(struct page *page, struct list_head *list,
}
local_irq_enable();
if (nr_dropped)
shmem_uncharge(head->mapping->host, nr_dropped);
remap_page(folio, nr);
if (PageSwapCache(head)) {

13
mm/khugepaged.c
View File

@ -1955,10 +1955,6 @@ static int collapse_file(struct mm_struct *mm, unsigned long addr,
goto xa_locked;
}
}
if (!shmem_charge(mapping->host, 1)) {
result = SCAN_FAIL;
goto xa_locked;
}
nr_none++;
continue;
}
@ -2145,8 +2141,13 @@ xa_unlocked:
*/
try_to_unmap_flush();
if (result != SCAN_SUCCEED)
if (result == SCAN_SUCCEED && nr_none &&
!shmem_charge(mapping->host, nr_none))
result = SCAN_FAIL;
if (result != SCAN_SUCCEED) {
nr_none = 0;
goto rollback;
}
/*
* The old pages are locked, so they won't change anymore.
@ -2283,8 +2284,8 @@ rollback:
if (nr_none) {
xas_lock_irq(&xas);
mapping->nrpages -= nr_none;
shmem_uncharge(mapping->host, nr_none);
xas_unlock_irq(&xas);
shmem_uncharge(mapping->host, nr_none);
}
list_for_each_entry_safe(page, tmp, &pagelist, lru) {

19
mm/shmem.c
View File

@ -424,18 +424,20 @@ static void shmem_recalc_inode(struct inode *inode)
bool shmem_charge(struct inode *inode, long pages)
{
struct shmem_inode_info *info = SHMEM_I(inode);
unsigned long flags;
struct address_space *mapping = inode->i_mapping;
if (shmem_inode_acct_block(inode, pages))
return false;
/* nrpages adjustment first, then shmem_recalc_inode() when balanced */
inode->i_mapping->nrpages += pages;
xa_lock_irq(&mapping->i_pages);
mapping->nrpages += pages;
xa_unlock_irq(&mapping->i_pages);
spin_lock_irqsave(&info->lock, flags);
spin_lock_irq(&info->lock);
info->alloced += pages;
shmem_recalc_inode(inode);
spin_unlock_irqrestore(&info->lock, flags);
spin_unlock_irq(&info->lock);
return true;
}
@ -443,16 +445,13 @@ bool shmem_charge(struct inode *inode, long pages)
void shmem_uncharge(struct inode *inode, long pages)
{
struct shmem_inode_info *info = SHMEM_I(inode);
unsigned long flags;
/* nrpages adjustment done by __filemap_remove_folio() or caller */
spin_lock_irqsave(&info->lock, flags);
info->alloced -= pages;
spin_lock_irq(&info->lock);
shmem_recalc_inode(inode);
spin_unlock_irqrestore(&info->lock, flags);
shmem_inode_unacct_blocks(inode, pages);
/* which has called shmem_inode_unacct_blocks() if necessary */
spin_unlock_irq(&info->lock);
}
/*