diff options
Diffstat (limited to 'mm/shmem.c')
| -rw-r--r-- | mm/shmem.c | 28 |
1 files changed, 28 insertions, 0 deletions
diff --git a/mm/shmem.c b/mm/shmem.c index b9255c1e7498..c45eaf04396e 100644 --- a/mm/shmem.c +++ b/mm/shmem.c @@ -948,6 +948,15 @@ static void shmem_undo_range(struct inode *inode, loff_t lstart, loff_t lend, index++; } + /* + * When undoing a failed fallocate, we want none of the partial folio + * zeroing and splitting below, but shall want to truncate the whole + * folio when !uptodate indicates that it was added by this fallocate, + * even when [lstart, lend] covers only a part of the folio. + */ + if (unfalloc) + goto whole_folios; + same_folio = (lstart >> PAGE_SHIFT) == (lend >> PAGE_SHIFT); folio = shmem_get_partial_folio(inode, lstart >> PAGE_SHIFT); if (folio) { @@ -973,6 +982,8 @@ static void shmem_undo_range(struct inode *inode, loff_t lstart, loff_t lend, folio_put(folio); } +whole_folios: + index = start; while (index < end) { cond_resched(); @@ -2424,9 +2435,26 @@ int shmem_mfill_atomic_pte(struct mm_struct *dst_mm, if (!zeropage) { /* COPY */ page_kaddr = kmap_local_folio(folio, 0); + /* + * The read mmap_lock is held here. Despite the + * mmap_lock being read recursive a deadlock is still + * possible if a writer has taken a lock. For example: + * + * process A thread 1 takes read lock on own mmap_lock + * process A thread 2 calls mmap, blocks taking write lock + * process B thread 1 takes page fault, read lock on own mmap lock + * process B thread 2 calls mmap, blocks taking write lock + * process A thread 1 blocks taking read lock on process B + * process B thread 1 blocks taking read lock on process A + * + * Disable page faults to prevent potential deadlock + * and retry the copy outside the mmap_lock. + */ + pagefault_disable(); ret = copy_from_user(page_kaddr, (const void __user *)src_addr, PAGE_SIZE); + pagefault_enable(); kunmap_local(page_kaddr); /* fallback to copy_from_user outside mmap_lock */ |