From 066e053fe208a3b83ee89dc5a192146add688861 Mon Sep 17 00:00:00 2001 From: Amir Goldstein Date: Wed, 12 Mar 2025 08:38:47 +0100 Subject: [PATCH 1/6] fsnotify: add pre-content hooks on mmap() Pre-content hooks in page faults introduces potential deadlock of HSM handler in userspace with filesystem freezing. The requirement with pre-content event is that for every accessed file range an event covering at least this range will be generated at least once before the file data is accesses. In preparation to disabling pre-content event hooks on page faults, add pre-content hooks at mmap() variants for the entire mmaped range, so HSM can fill content when user requests to map a portion of the file. Note that exec() variant also calls vm_mmap_pgoff() internally to map code sections, so pre-content hooks are also generated in this case. Link: https://lore.kernel.org/linux-fsdevel/7ehxrhbvehlrjwvrduoxsao5k3x4aw275patsb3krkwuq573yv@o2hskrfawbnc/ Suggested-by: Josef Bacik Signed-off-by: Amir Goldstein Signed-off-by: Jan Kara Link: https://patch.msgid.link/20250312073852.2123409-2-amir73il@gmail.com --- include/linux/fsnotify.h | 21 +++++++++++++++++++++ mm/util.c | 3 +++ 2 files changed, 24 insertions(+) diff --git a/include/linux/fsnotify.h b/include/linux/fsnotify.h index 6a33288bd6a1..83d3ac97f826 100644 --- a/include/linux/fsnotify.h +++ b/include/linux/fsnotify.h @@ -170,6 +170,21 @@ static inline int fsnotify_file_area_perm(struct file *file, int perm_mask, return fsnotify_path(&file->f_path, FS_ACCESS_PERM); } +/* + * fsnotify_mmap_perm - permission hook before mmap of file range + */ +static inline int fsnotify_mmap_perm(struct file *file, int prot, + const loff_t off, size_t len) +{ + /* + * mmap() generates only pre-content events. + */ + if (!file || likely(!FMODE_FSNOTIFY_HSM(file->f_mode))) + return 0; + + return fsnotify_pre_content(&file->f_path, &off, len); +} + /* * fsnotify_truncate_perm - permission hook before file truncate */ @@ -223,6 +238,12 @@ static inline int fsnotify_file_area_perm(struct file *file, int perm_mask, return 0; } +static inline int fsnotify_mmap_perm(struct file *file, int prot, + const loff_t off, size_t len) +{ + return 0; +} + static inline int fsnotify_truncate_perm(const struct path *path, loff_t length) { return 0; diff --git a/mm/util.c b/mm/util.c index b6b9684a1438..8c965474d329 100644 --- a/mm/util.c +++ b/mm/util.c @@ -23,6 +23,7 @@ #include #include #include +#include #include @@ -569,6 +570,8 @@ unsigned long vm_mmap_pgoff(struct file *file, unsigned long addr, LIST_HEAD(uf); ret = security_mmap_file(file, prot, flag); + if (!ret) + ret = fsnotify_mmap_perm(file, prot, pgoff >> PAGE_SHIFT, len); if (!ret) { if (mmap_write_lock_killable(mm)) return -EINTR; From bc71aab4513f7fecd23c051703ef5adea2230a54 Mon Sep 17 00:00:00 2001 From: Amir Goldstein Date: Wed, 12 Mar 2025 08:38:48 +0100 Subject: [PATCH 2/6] Revert "ext4: add pre-content fsnotify hook for DAX faults" This reverts commit bb480760ffc7018e21ee6f60241c2b99ff26ee0e. Signed-off-by: Amir Goldstein Signed-off-by: Jan Kara Link: https://patch.msgid.link/20250312073852.2123409-3-amir73il@gmail.com --- fs/ext4/file.c | 3 --- 1 file changed, 3 deletions(-) diff --git a/fs/ext4/file.c b/fs/ext4/file.c index a5205149adba..3bd96c3d4cd0 100644 --- a/fs/ext4/file.c +++ b/fs/ext4/file.c @@ -756,9 +756,6 @@ static vm_fault_t ext4_dax_huge_fault(struct vm_fault *vmf, unsigned int order) return VM_FAULT_SIGBUS; } } else { - result = filemap_fsnotify_fault(vmf); - if (unlikely(result)) - return result; filemap_invalidate_lock_shared(mapping); } result = dax_iomap_fault(vmf, order, &pfn, &error, &ext4_iomap_ops); From 27773ce1776279ed3220a34d2e6bfcecaee7fc66 Mon Sep 17 00:00:00 2001 From: Amir Goldstein Date: Wed, 12 Mar 2025 08:38:49 +0100 Subject: [PATCH 3/6] Revert "xfs: add pre-content fsnotify hook for DAX faults" This reverts commit 7f4796a46571ced5d3d5b0942e1bfea1eedaaecd. Signed-off-by: Amir Goldstein Signed-off-by: Jan Kara Link: https://patch.msgid.link/20250312073852.2123409-4-amir73il@gmail.com --- fs/xfs/xfs_file.c | 13 ------------- 1 file changed, 13 deletions(-) diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c index f7a7d89c345e..9a435b1ff264 100644 --- a/fs/xfs/xfs_file.c +++ b/fs/xfs/xfs_file.c @@ -1451,9 +1451,6 @@ xfs_dax_read_fault( trace_xfs_read_fault(ip, order); - ret = filemap_fsnotify_fault(vmf); - if (unlikely(ret)) - return ret; xfs_ilock(ip, XFS_MMAPLOCK_SHARED); ret = xfs_dax_fault_locked(vmf, order, false); xfs_iunlock(ip, XFS_MMAPLOCK_SHARED); @@ -1482,16 +1479,6 @@ xfs_write_fault( vm_fault_t ret; trace_xfs_write_fault(ip, order); - /* - * Usually we get here from ->page_mkwrite callback but in case of DAX - * we will get here also for ordinary write fault. Handle HSM - * notifications for that case. - */ - if (IS_DAX(inode)) { - ret = filemap_fsnotify_fault(vmf); - if (unlikely(ret)) - return ret; - } sb_start_pagefault(inode->i_sb); file_update_time(vmf->vma->vm_file); From 955fbe0ef19df4197595a98d0906c94025c4beef Mon Sep 17 00:00:00 2001 From: Amir Goldstein Date: Wed, 12 Mar 2025 08:38:50 +0100 Subject: [PATCH 4/6] Revert "fsnotify: generate pre-content permission event on page fault" This reverts commit 8392bc2ff8c8bf7c4c5e6dfa71ccd893a3c046f6. In the use case of buffered write whose input buffer is mmapped file on a filesystem with a pre-content mark, the prefaulting of the buffer can happen under the filesystem freeze protection (obtained in vfs_write()) which breaks assumptions of pre-content hook and introduces potential deadlock of HSM handler in userspace with filesystem freezing. Now that we have pre-content hooks at file mmap() time, disable the pre-content event hooks on page fault to avoid the potential deadlock. Reported-by: syzbot+7229071b47908b19d5b7@syzkaller.appspotmail.com Closes: https://lore.kernel.org/linux-fsdevel/7ehxrhbvehlrjwvrduoxsao5k3x4aw275patsb3krkwuq573yv@o2hskrfawbnc/ Fixes: 8392bc2ff8c8 ("fsnotify: generate pre-content permission event on page fault") Signed-off-by: Amir Goldstein Signed-off-by: Jan Kara Link: https://patch.msgid.link/20250312073852.2123409-5-amir73il@gmail.com --- include/linux/mm.h | 1 - mm/filemap.c | 74 ---------------------------------------------- mm/nommu.c | 7 ----- 3 files changed, 82 deletions(-) diff --git a/include/linux/mm.h b/include/linux/mm.h index 7b1068ddcbb7..8483e09aeb2c 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -3420,7 +3420,6 @@ extern vm_fault_t filemap_fault(struct vm_fault *vmf); extern vm_fault_t filemap_map_pages(struct vm_fault *vmf, pgoff_t start_pgoff, pgoff_t end_pgoff); extern vm_fault_t filemap_page_mkwrite(struct vm_fault *vmf); -extern vm_fault_t filemap_fsnotify_fault(struct vm_fault *vmf); extern unsigned long stack_guard_gap; /* Generic expand stack which grows the stack according to GROWS{UP,DOWN} */ diff --git a/mm/filemap.c b/mm/filemap.c index 2974691fdfad..ff5fcdd96136 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -47,7 +47,6 @@ #include #include #include -#include #include #include #include "internal.h" @@ -3336,48 +3335,6 @@ static vm_fault_t filemap_fault_recheck_pte_none(struct vm_fault *vmf) return ret; } -/** - * filemap_fsnotify_fault - maybe emit a pre-content event. - * @vmf: struct vm_fault containing details of the fault. - * - * If we have a pre-content watch on this file we will emit an event for this - * range. If we return anything the fault caller should return immediately, we - * will return VM_FAULT_RETRY if we had to emit an event, which will trigger the - * fault again and then the fault handler will run the second time through. - * - * Return: a bitwise-OR of %VM_FAULT_ codes, 0 if nothing happened. - */ -vm_fault_t filemap_fsnotify_fault(struct vm_fault *vmf) -{ - struct file *fpin = NULL; - int mask = (vmf->flags & FAULT_FLAG_WRITE) ? MAY_WRITE : MAY_ACCESS; - loff_t pos = vmf->pgoff >> PAGE_SHIFT; - size_t count = PAGE_SIZE; - int err; - - /* - * We already did this and now we're retrying with everything locked, - * don't emit the event and continue. - */ - if (vmf->flags & FAULT_FLAG_TRIED) - return 0; - - /* No watches, we're done. */ - if (likely(!FMODE_FSNOTIFY_HSM(vmf->vma->vm_file->f_mode))) - return 0; - - fpin = maybe_unlock_mmap_for_io(vmf, fpin); - if (!fpin) - return VM_FAULT_SIGBUS; - - err = fsnotify_file_area_perm(fpin, mask, &pos, count); - fput(fpin); - if (err) - return VM_FAULT_SIGBUS; - return VM_FAULT_RETRY; -} -EXPORT_SYMBOL_GPL(filemap_fsnotify_fault); - /** * filemap_fault - read in file data for page fault handling * @vmf: struct vm_fault containing details of the fault @@ -3481,37 +3438,6 @@ vm_fault_t filemap_fault(struct vm_fault *vmf) * or because readahead was otherwise unable to retrieve it. */ if (unlikely(!folio_test_uptodate(folio))) { - /* - * If this is a precontent file we have can now emit an event to - * try and populate the folio. - */ - if (!(vmf->flags & FAULT_FLAG_TRIED) && - unlikely(FMODE_FSNOTIFY_HSM(file->f_mode))) { - loff_t pos = folio_pos(folio); - size_t count = folio_size(folio); - - /* We're NOWAIT, we have to retry. */ - if (vmf->flags & FAULT_FLAG_RETRY_NOWAIT) { - folio_unlock(folio); - goto out_retry; - } - - if (mapping_locked) - filemap_invalidate_unlock_shared(mapping); - mapping_locked = false; - - folio_unlock(folio); - fpin = maybe_unlock_mmap_for_io(vmf, fpin); - if (!fpin) - goto out_retry; - - error = fsnotify_file_area_perm(fpin, MAY_ACCESS, &pos, - count); - if (error) - ret = VM_FAULT_SIGBUS; - goto out_retry; - } - /* * If the invalidate lock is not held, the folio was in cache * and uptodate and now it is not. Strange but possible since we diff --git a/mm/nommu.c b/mm/nommu.c index baa79abdaf03..9cb6e99215e2 100644 --- a/mm/nommu.c +++ b/mm/nommu.c @@ -1613,13 +1613,6 @@ int remap_vmalloc_range(struct vm_area_struct *vma, void *addr, } EXPORT_SYMBOL(remap_vmalloc_range); -vm_fault_t filemap_fsnotify_fault(struct vm_fault *vmf) -{ - BUG(); - return 0; -} -EXPORT_SYMBOL_GPL(filemap_fsnotify_fault); - vm_fault_t filemap_fault(struct vm_fault *vmf) { BUG(); From 4f4dc3a9378bc2e6bcf331ee9e65a21abf67e7e0 Mon Sep 17 00:00:00 2001 From: Amir Goldstein Date: Wed, 12 Mar 2025 08:38:51 +0100 Subject: [PATCH 5/6] Revert "mm: don't allow huge faults for files with pre content watches" This reverts commit 20bf82a898b65c129af76deb96a1b415d3098a28. Signed-off-by: Amir Goldstein Signed-off-by: Jan Kara Link: https://patch.msgid.link/20250312073852.2123409-6-amir73il@gmail.com --- mm/memory.c | 19 ------------------- 1 file changed, 19 deletions(-) diff --git a/mm/memory.c b/mm/memory.c index b9661ccfa64f..fb7b8dc75167 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -76,7 +76,6 @@ #include #include #include -#include #include @@ -5750,17 +5749,8 @@ static vm_fault_t do_numa_page(struct vm_fault *vmf) static inline vm_fault_t create_huge_pmd(struct vm_fault *vmf) { struct vm_area_struct *vma = vmf->vma; - if (vma_is_anonymous(vma)) return do_huge_pmd_anonymous_page(vmf); - /* - * Currently we just emit PAGE_SIZE for our fault events, so don't allow - * a huge fault if we have a pre content watch on this file. This would - * be trivial to support, but there would need to be tests to ensure - * this works properly and those don't exist currently. - */ - if (unlikely(FMODE_FSNOTIFY_HSM(vma->vm_file->f_mode))) - return VM_FAULT_FALLBACK; if (vma->vm_ops->huge_fault) return vma->vm_ops->huge_fault(vmf, PMD_ORDER); return VM_FAULT_FALLBACK; @@ -5784,9 +5774,6 @@ static inline vm_fault_t wp_huge_pmd(struct vm_fault *vmf) } if (vma->vm_flags & (VM_SHARED | VM_MAYSHARE)) { - /* See comment in create_huge_pmd. */ - if (unlikely(FMODE_FSNOTIFY_HSM(vma->vm_file->f_mode))) - goto split; if (vma->vm_ops->huge_fault) { ret = vma->vm_ops->huge_fault(vmf, PMD_ORDER); if (!(ret & VM_FAULT_FALLBACK)) @@ -5809,9 +5796,6 @@ static vm_fault_t create_huge_pud(struct vm_fault *vmf) /* No support for anonymous transparent PUD pages yet */ if (vma_is_anonymous(vma)) return VM_FAULT_FALLBACK; - /* See comment in create_huge_pmd. */ - if (unlikely(FMODE_FSNOTIFY_HSM(vma->vm_file->f_mode))) - return VM_FAULT_FALLBACK; if (vma->vm_ops->huge_fault) return vma->vm_ops->huge_fault(vmf, PUD_ORDER); #endif /* CONFIG_TRANSPARENT_HUGEPAGE */ @@ -5829,9 +5813,6 @@ static vm_fault_t wp_huge_pud(struct vm_fault *vmf, pud_t orig_pud) if (vma_is_anonymous(vma)) goto split; if (vma->vm_flags & (VM_SHARED | VM_MAYSHARE)) { - /* See comment in create_huge_pmd. */ - if (unlikely(FMODE_FSNOTIFY_HSM(vma->vm_file->f_mode))) - goto split; if (vma->vm_ops->huge_fault) { ret = vma->vm_ops->huge_fault(vmf, PUD_ORDER); if (!(ret & VM_FAULT_FALLBACK)) From 252256e416deb255607f0c4a69e7cfec079e5d61 Mon Sep 17 00:00:00 2001 From: Amir Goldstein Date: Wed, 12 Mar 2025 08:38:52 +0100 Subject: [PATCH 6/6] Revert "fanotify: disable readahead if we have pre-content watches" This reverts commit fac84846a28c0950d4433118b3dffd44306df62d. Signed-off-by: Amir Goldstein Signed-off-by: Jan Kara Link: https://patch.msgid.link/20250312073852.2123409-7-amir73il@gmail.com --- mm/filemap.c | 12 ------------ mm/readahead.c | 14 -------------- 2 files changed, 26 deletions(-) diff --git a/mm/filemap.c b/mm/filemap.c index ff5fcdd96136..6d616bb9001e 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -3197,14 +3197,6 @@ static struct file *do_sync_mmap_readahead(struct vm_fault *vmf) unsigned long vm_flags = vmf->vma->vm_flags; unsigned int mmap_miss; - /* - * If we have pre-content watches we need to disable readahead to make - * sure that we don't populate our mapping with 0 filled pages that we - * never emitted an event for. - */ - if (unlikely(FMODE_FSNOTIFY_HSM(file->f_mode))) - return fpin; - #ifdef CONFIG_TRANSPARENT_HUGEPAGE /* Use the readahead code, even if readahead is disabled */ if ((vm_flags & VM_HUGEPAGE) && HPAGE_PMD_ORDER <= MAX_PAGECACHE_ORDER) { @@ -3273,10 +3265,6 @@ static struct file *do_async_mmap_readahead(struct vm_fault *vmf, struct file *fpin = NULL; unsigned int mmap_miss; - /* See comment in do_sync_mmap_readahead. */ - if (unlikely(FMODE_FSNOTIFY_HSM(file->f_mode))) - return fpin; - /* If we don't want any read-ahead, don't bother */ if (vmf->vma->vm_flags & VM_RAND_READ || !ra->ra_pages) return fpin; diff --git a/mm/readahead.c b/mm/readahead.c index 220155a5c964..6a4e96b69702 100644 --- a/mm/readahead.c +++ b/mm/readahead.c @@ -128,7 +128,6 @@ #include #include #include -#include #include "internal.h" @@ -558,15 +557,6 @@ void page_cache_sync_ra(struct readahead_control *ractl, unsigned long max_pages, contig_count; pgoff_t prev_index, miss; - /* - * If we have pre-content watches we need to disable readahead to make - * sure that we don't find 0 filled pages in cache that we never emitted - * events for. Filesystems supporting HSM must make sure to not call - * this function with ractl->file unset for files handled by HSM. - */ - if (ractl->file && unlikely(FMODE_FSNOTIFY_HSM(ractl->file->f_mode))) - return; - /* * Even if readahead is disabled, issue this request as readahead * as we'll need it to satisfy the requested range. The forced @@ -645,10 +635,6 @@ void page_cache_async_ra(struct readahead_control *ractl, if (!ra->ra_pages) return; - /* See the comment in page_cache_sync_ra. */ - if (ractl->file && unlikely(FMODE_FSNOTIFY_HSM(ractl->file->f_mode))) - return; - /* * Same bit is used for PG_readahead and PG_reclaim. */