ntfs_check_logfile() calls kmap_local_folio() on every iteration of its search loop but calls kunmap_local() only when it moves on to the next folio. With 4 KiB pages the positions 0, 512, 1024 and 2048 are all in the first page, so every mount leaves three entries on the kmap_local stack of the mounting task. 64-bit kernels do not notice, kmap_local_folio() does not touch the stack there. 32-bit kernels with HIGHMEM return from mount(2) with the mappings in place. With the generic entry code that is a warning: DEBUG_LOCKS_WARN_ON(current->kmap_ctrl.idx) WARNING: include/linux/highmem-internal.h:17 at __do_fast_syscall_32+0x21e/0x550 The stack has 16 slots, so a process that mounts ntfs volumes five times hits the BUG_ON() in kmap_local_idx_push() during the fifth mount: kernel BUG at mm/highmem.c:480! Map each page once, when it is read, and unmap that address. Fixes: 5218cd102aec ("ntfs: update misc operations") Cc: stable@vger.kernel.org Assisted-by: LLM Signed-off-by: Karl Mehltretter --- Tested on top of patch 1 in QEMU with a fresh mkntfs volume and a small program that calls mount(2) and umount(2) eight times in one process: - 32-bit ARM (multi_v7_defconfig plus KCOV, virt, 1 GiB RAM, 256 MiB highmem) and x86-32 (i386_defconfig plus HIGHMEM4G, 2 GiB RAM): without this patch mounts one to four succeed and the fifth hits the BUG_ON() in kmap_local_idx_push() on both. With it all eight complete. - x86-32 no longer warns when mount(2) returns. Three mounts in a row with mount(8) are clean on both. The other kmap_local_folio() loops in fs/ntfs (lcnalloc.c, mft.c, bitmap.c, compress.c) unmap on every path before they map again. fs/ntfs/logfile.c | 11 ++++++----- 1 file changed, 6 insertions(+), 5 deletions(-) diff --git a/fs/ntfs/logfile.c b/fs/ntfs/logfile.c index 1404664dacc0..ce38ce87f8fc 100644 --- a/fs/ntfs/logfile.c +++ b/fs/ntfs/logfile.c @@ -457,7 +457,7 @@ bool ntfs_check_logfile(struct inode *log_vi, struct restart_page_header **rp) struct ntfs_volume *vol = NTFS_SB(log_vi->i_sb); struct address_space *mapping = log_vi->i_mapping; struct folio *folio = NULL; - u8 *kaddr = NULL; + u8 *kaddr = NULL, *kbase = NULL; struct restart_page_header *rstr1_ph = NULL; struct restart_page_header *rstr2_ph = NULL; int log_page_size, err; @@ -511,7 +511,7 @@ bool ntfs_check_logfile(struct inode *log_vi, struct restart_page_header **rp) if (!folio || folio->index != idx) { if (folio) { - kunmap_local(kaddr); + kunmap_local(kbase); folio_put(folio); } folio = read_mapping_folio(mapping, idx, NULL); @@ -520,8 +520,9 @@ bool ntfs_check_logfile(struct inode *log_vi, struct restart_page_header **rp) idx); goto err_out; } + kbase = kmap_local_folio(folio, 0); } - kaddr = (u8 *)kmap_local_folio(folio, 0) + (pos & ~PAGE_MASK); + kaddr = kbase + (pos & ~PAGE_MASK); /* * A non-empty block means the logfile is not empty while an * empty block after a non-empty block has been encountered @@ -574,7 +575,7 @@ bool ntfs_check_logfile(struct inode *log_vi, struct restart_page_header **rp) * find a valid one further in the file. */ if (err != -EINVAL) { - kunmap_local(kaddr); + kunmap_local(kbase); folio_put(folio); goto err_out; } @@ -583,7 +584,7 @@ bool ntfs_check_logfile(struct inode *log_vi, struct restart_page_header **rp) pos = NTFS_BLOCK_SIZE >> 1; } if (folio) { - kunmap_local(kaddr); + kunmap_local(kbase); folio_put(folio); } if (logfile_is_empty) { -- 2.53.0