| Message ID | b8c3f0d9ed6d23f9a636919e28293cdbbe22e0db.1723144881.git.josef@toxicpanda.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | fanotify: add pre-content hooks | expand |
On Thu, Aug 8, 2024 at 9:28 PM Josef Bacik <josef@toxicpanda.com> wrote: > > FS_PRE_ACCESS or FS_PRE_MODIFY will be generated on page fault depending > on the faulting method. > > This pre-content event is meant to be used by hierarchical storage > managers that want to fill in the file content on first read access. > > Signed-off-by: Josef Bacik <josef@toxicpanda.com> > --- > include/linux/mm.h | 2 + > mm/filemap.c | 97 ++++++++++++++++++++++++++++++++++++++++++---- > 2 files changed, 92 insertions(+), 7 deletions(-) > > diff --git a/include/linux/mm.h b/include/linux/mm.h > index ab3d78116043..c33f3b7f7261 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -3503,6 +3503,8 @@ 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_maybe_emit_fsnotify_event(struct vm_fault *vmf, > + struct file **fpin); > > 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 8b1684b62177..3d232166b051 100644 > --- a/mm/filemap.c > +++ b/mm/filemap.c > @@ -46,6 +46,7 @@ > #include <linux/pipe_fs_i.h> > #include <linux/splice.h> > #include <linux/rcupdate_wait.h> > +#include <linux/fsnotify.h> > #include <asm/pgalloc.h> > #include <asm/tlbflush.h> > #include "internal.h" > @@ -3112,13 +3113,13 @@ static int lock_folio_maybe_drop_mmap(struct vm_fault *vmf, struct folio *folio, > * that. If we didn't pin a file then we return NULL. The file that is > * returned needs to be fput()'ed when we're done with it. > */ > -static struct file *do_sync_mmap_readahead(struct vm_fault *vmf) > +static struct file *do_sync_mmap_readahead(struct vm_fault *vmf, > + struct file *fpin) > { > struct file *file = vmf->vma->vm_file; > struct file_ra_state *ra = &file->f_ra; > struct address_space *mapping = file->f_mapping; > DEFINE_READAHEAD(ractl, file, ra, mapping, vmf->pgoff); > - struct file *fpin = NULL; > unsigned long vm_flags = vmf->vma->vm_flags; > unsigned int mmap_miss; > > @@ -3190,12 +3191,12 @@ static struct file *do_sync_mmap_readahead(struct vm_fault *vmf) > * was pinned if we have to drop the mmap_lock in order to do IO. > */ > static struct file *do_async_mmap_readahead(struct vm_fault *vmf, > - struct folio *folio) > + struct folio *folio, > + struct file *fpin) > { > struct file *file = vmf->vma->vm_file; > struct file_ra_state *ra = &file->f_ra; > DEFINE_READAHEAD(ractl, file, ra, file->f_mapping, vmf->pgoff); > - struct file *fpin = NULL; > unsigned int mmap_miss; > > /* See comment in do_sync_mmap_readahead. */ > @@ -3260,6 +3261,72 @@ static vm_fault_t filemap_fault_recheck_pte_none(struct vm_fault *vmf) > return ret; > } > > +/** > + * filemap_maybe_emit_fsnotify_event - maybe emit a pre-content event. > + * @vmf: struct vm_fault containing details of the fault. > + * @fpin: pointer to the struct file pointer that may be pinned. > + * > + * If we have pre-content watches on this file we will need to emit an event for > + * this range. We will handle dropping the lock and emitting the event. > + * > + * If FAULT_FLAG_RETRY_NOWAIT is set then we'll return VM_FAULT_RETRY. > + * > + * If no event was emitted then *fpin will be NULL and we will return 0. > + * > + * If any error occurred we will return VM_FAULT_SIGBUS, *fpin could still be > + * set and will need to have fput() called on it. > + * > + * If we emitted the event then we will return 0 and *fpin will be set, this > + * must have fput() called on it, and the caller must call VM_FAULT_RETRY after > + * any other operations it does in order to re-fault the page and make sure the > + * appropriate locking is maintained. > + * > + * Return: the appropriate vm_fault_t return code, 0 on success. > + */ > +vm_fault_t filemap_maybe_emit_fsnotify_event(struct vm_fault *vmf, > + struct file **fpin) > +{ > + struct file *file = vmf->vma->vm_file; > + loff_t pos = vmf->pgoff << PAGE_SHIFT; > + int mask = (vmf->flags & FAULT_FLAG_WRITE) ? MAY_WRITE : MAY_READ; You missed my comment about using MAY_ACCESS here and alter fsnotify hook, so legacy FAN_ACCESS_PERM event won't be generated from page fault. Thanks, Amir. > + int ret; > + > + /* > + * 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, return NULL. */ > + if (!fsnotify_file_has_pre_content_watches(file)) > + return 0; > + > + /* We are NOWAIT, we can't wait, just return EAGAIN. */ > + if (vmf->flags & FAULT_FLAG_RETRY_NOWAIT) > + return VM_FAULT_RETRY; > + > + /* > + * If this fails then we're not allowed to drop the fault lock, return a > + * SIGBUS so we don't errantly populate pagecache with bogus data for > + * this file. > + */ > + *fpin = maybe_unlock_mmap_for_io(vmf, *fpin); > + if (*fpin == NULL) > + return VM_FAULT_SIGBUS | VM_FAULT_RETRY; > + > + /* > + * We can't fput(*fpin) at this point because we could have been passed > + * in fpin from a previous call. > + */ > + ret = fsnotify_file_area_perm(*fpin, mask, &pos, PAGE_SIZE); > + if (ret) > + return VM_FAULT_SIGBUS; > + > + return 0; > +} > +EXPORT_SYMBOL_GPL(filemap_maybe_emit_fsnotify_event); > + > /** > * filemap_fault - read in file data for page fault handling > * @vmf: struct vm_fault containing details of the fault > @@ -3299,6 +3366,19 @@ vm_fault_t filemap_fault(struct vm_fault *vmf) > if (unlikely(index >= max_idx)) > return VM_FAULT_SIGBUS; > > + /* > + * If we have pre-content watchers then we need to generate events on > + * page fault so that we can populate any data before the fault. > + */ > + ret = filemap_maybe_emit_fsnotify_event(vmf, &fpin); > + if (unlikely(ret)) { > + if (fpin) { > + fput(fpin); > + ret |= VM_FAULT_RETRY; > + } > + return ret; > + } > + > /* > * Do we have something in the page cache already? > */ > @@ -3309,21 +3389,24 @@ vm_fault_t filemap_fault(struct vm_fault *vmf) > * the lock. > */ > if (!(vmf->flags & FAULT_FLAG_TRIED)) > - fpin = do_async_mmap_readahead(vmf, folio); > + fpin = do_async_mmap_readahead(vmf, folio, fpin); > if (unlikely(!folio_test_uptodate(folio))) { > filemap_invalidate_lock_shared(mapping); > mapping_locked = true; > } > } else { > ret = filemap_fault_recheck_pte_none(vmf); > - if (unlikely(ret)) > + if (unlikely(ret)) { > + if (fpin) > + goto out_retry; > return ret; > + } > > /* No page in the page cache at all */ > count_vm_event(PGMAJFAULT); > count_memcg_event_mm(vmf->vma->vm_mm, PGMAJFAULT); > ret = VM_FAULT_MAJOR; > - fpin = do_sync_mmap_readahead(vmf); > + fpin = do_sync_mmap_readahead(vmf, fpin); > retry_find: > /* > * See comment in filemap_create_folio() why we need > -- > 2.43.0 >
On Fri, Aug 09, 2024 at 12:34:34PM +0200, Amir Goldstein wrote: > On Thu, Aug 8, 2024 at 9:28 PM Josef Bacik <josef@toxicpanda.com> wrote: > > > > FS_PRE_ACCESS or FS_PRE_MODIFY will be generated on page fault depending > > on the faulting method. > > > > This pre-content event is meant to be used by hierarchical storage > > managers that want to fill in the file content on first read access. > > > > Signed-off-by: Josef Bacik <josef@toxicpanda.com> > > --- > > include/linux/mm.h | 2 + > > mm/filemap.c | 97 ++++++++++++++++++++++++++++++++++++++++++---- > > 2 files changed, 92 insertions(+), 7 deletions(-) > > > > diff --git a/include/linux/mm.h b/include/linux/mm.h > > index ab3d78116043..c33f3b7f7261 100644 > > --- a/include/linux/mm.h > > +++ b/include/linux/mm.h > > @@ -3503,6 +3503,8 @@ 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_maybe_emit_fsnotify_event(struct vm_fault *vmf, > > + struct file **fpin); > > > > 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 8b1684b62177..3d232166b051 100644 > > --- a/mm/filemap.c > > +++ b/mm/filemap.c > > @@ -46,6 +46,7 @@ > > #include <linux/pipe_fs_i.h> > > #include <linux/splice.h> > > #include <linux/rcupdate_wait.h> > > +#include <linux/fsnotify.h> > > #include <asm/pgalloc.h> > > #include <asm/tlbflush.h> > > #include "internal.h" > > @@ -3112,13 +3113,13 @@ static int lock_folio_maybe_drop_mmap(struct vm_fault *vmf, struct folio *folio, > > * that. If we didn't pin a file then we return NULL. The file that is > > * returned needs to be fput()'ed when we're done with it. > > */ > > -static struct file *do_sync_mmap_readahead(struct vm_fault *vmf) > > +static struct file *do_sync_mmap_readahead(struct vm_fault *vmf, > > + struct file *fpin) > > { > > struct file *file = vmf->vma->vm_file; > > struct file_ra_state *ra = &file->f_ra; > > struct address_space *mapping = file->f_mapping; > > DEFINE_READAHEAD(ractl, file, ra, mapping, vmf->pgoff); > > - struct file *fpin = NULL; > > unsigned long vm_flags = vmf->vma->vm_flags; > > unsigned int mmap_miss; > > > > @@ -3190,12 +3191,12 @@ static struct file *do_sync_mmap_readahead(struct vm_fault *vmf) > > * was pinned if we have to drop the mmap_lock in order to do IO. > > */ > > static struct file *do_async_mmap_readahead(struct vm_fault *vmf, > > - struct folio *folio) > > + struct folio *folio, > > + struct file *fpin) > > { > > struct file *file = vmf->vma->vm_file; > > struct file_ra_state *ra = &file->f_ra; > > DEFINE_READAHEAD(ractl, file, ra, file->f_mapping, vmf->pgoff); > > - struct file *fpin = NULL; > > unsigned int mmap_miss; > > > > /* See comment in do_sync_mmap_readahead. */ > > @@ -3260,6 +3261,72 @@ static vm_fault_t filemap_fault_recheck_pte_none(struct vm_fault *vmf) > > return ret; > > } > > > > +/** > > + * filemap_maybe_emit_fsnotify_event - maybe emit a pre-content event. > > + * @vmf: struct vm_fault containing details of the fault. > > + * @fpin: pointer to the struct file pointer that may be pinned. > > + * > > + * If we have pre-content watches on this file we will need to emit an event for > > + * this range. We will handle dropping the lock and emitting the event. > > + * > > + * If FAULT_FLAG_RETRY_NOWAIT is set then we'll return VM_FAULT_RETRY. > > + * > > + * If no event was emitted then *fpin will be NULL and we will return 0. > > + * > > + * If any error occurred we will return VM_FAULT_SIGBUS, *fpin could still be > > + * set and will need to have fput() called on it. > > + * > > + * If we emitted the event then we will return 0 and *fpin will be set, this > > + * must have fput() called on it, and the caller must call VM_FAULT_RETRY after > > + * any other operations it does in order to re-fault the page and make sure the > > + * appropriate locking is maintained. > > + * > > + * Return: the appropriate vm_fault_t return code, 0 on success. > > + */ > > +vm_fault_t filemap_maybe_emit_fsnotify_event(struct vm_fault *vmf, > > + struct file **fpin) > > +{ > > + struct file *file = vmf->vma->vm_file; > > + loff_t pos = vmf->pgoff << PAGE_SHIFT; > > + int mask = (vmf->flags & FAULT_FLAG_WRITE) ? MAY_WRITE : MAY_READ; > > You missed my comment about using MAY_ACCESS here > and alter fsnotify hook, so legacy FAN_ACCESS_PERM event > won't be generated from page fault. I did miss that, I'll fix it up in v3, thanks! Josef
diff --git a/include/linux/mm.h b/include/linux/mm.h index ab3d78116043..c33f3b7f7261 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -3503,6 +3503,8 @@ 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_maybe_emit_fsnotify_event(struct vm_fault *vmf, + struct file **fpin); 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 8b1684b62177..3d232166b051 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -46,6 +46,7 @@ #include <linux/pipe_fs_i.h> #include <linux/splice.h> #include <linux/rcupdate_wait.h> +#include <linux/fsnotify.h> #include <asm/pgalloc.h> #include <asm/tlbflush.h> #include "internal.h" @@ -3112,13 +3113,13 @@ static int lock_folio_maybe_drop_mmap(struct vm_fault *vmf, struct folio *folio, * that. If we didn't pin a file then we return NULL. The file that is * returned needs to be fput()'ed when we're done with it. */ -static struct file *do_sync_mmap_readahead(struct vm_fault *vmf) +static struct file *do_sync_mmap_readahead(struct vm_fault *vmf, + struct file *fpin) { struct file *file = vmf->vma->vm_file; struct file_ra_state *ra = &file->f_ra; struct address_space *mapping = file->f_mapping; DEFINE_READAHEAD(ractl, file, ra, mapping, vmf->pgoff); - struct file *fpin = NULL; unsigned long vm_flags = vmf->vma->vm_flags; unsigned int mmap_miss; @@ -3190,12 +3191,12 @@ static struct file *do_sync_mmap_readahead(struct vm_fault *vmf) * was pinned if we have to drop the mmap_lock in order to do IO. */ static struct file *do_async_mmap_readahead(struct vm_fault *vmf, - struct folio *folio) + struct folio *folio, + struct file *fpin) { struct file *file = vmf->vma->vm_file; struct file_ra_state *ra = &file->f_ra; DEFINE_READAHEAD(ractl, file, ra, file->f_mapping, vmf->pgoff); - struct file *fpin = NULL; unsigned int mmap_miss; /* See comment in do_sync_mmap_readahead. */ @@ -3260,6 +3261,72 @@ static vm_fault_t filemap_fault_recheck_pte_none(struct vm_fault *vmf) return ret; } +/** + * filemap_maybe_emit_fsnotify_event - maybe emit a pre-content event. + * @vmf: struct vm_fault containing details of the fault. + * @fpin: pointer to the struct file pointer that may be pinned. + * + * If we have pre-content watches on this file we will need to emit an event for + * this range. We will handle dropping the lock and emitting the event. + * + * If FAULT_FLAG_RETRY_NOWAIT is set then we'll return VM_FAULT_RETRY. + * + * If no event was emitted then *fpin will be NULL and we will return 0. + * + * If any error occurred we will return VM_FAULT_SIGBUS, *fpin could still be + * set and will need to have fput() called on it. + * + * If we emitted the event then we will return 0 and *fpin will be set, this + * must have fput() called on it, and the caller must call VM_FAULT_RETRY after + * any other operations it does in order to re-fault the page and make sure the + * appropriate locking is maintained. + * + * Return: the appropriate vm_fault_t return code, 0 on success. + */ +vm_fault_t filemap_maybe_emit_fsnotify_event(struct vm_fault *vmf, + struct file **fpin) +{ + struct file *file = vmf->vma->vm_file; + loff_t pos = vmf->pgoff << PAGE_SHIFT; + int mask = (vmf->flags & FAULT_FLAG_WRITE) ? MAY_WRITE : MAY_READ; + int ret; + + /* + * 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, return NULL. */ + if (!fsnotify_file_has_pre_content_watches(file)) + return 0; + + /* We are NOWAIT, we can't wait, just return EAGAIN. */ + if (vmf->flags & FAULT_FLAG_RETRY_NOWAIT) + return VM_FAULT_RETRY; + + /* + * If this fails then we're not allowed to drop the fault lock, return a + * SIGBUS so we don't errantly populate pagecache with bogus data for + * this file. + */ + *fpin = maybe_unlock_mmap_for_io(vmf, *fpin); + if (*fpin == NULL) + return VM_FAULT_SIGBUS | VM_FAULT_RETRY; + + /* + * We can't fput(*fpin) at this point because we could have been passed + * in fpin from a previous call. + */ + ret = fsnotify_file_area_perm(*fpin, mask, &pos, PAGE_SIZE); + if (ret) + return VM_FAULT_SIGBUS; + + return 0; +} +EXPORT_SYMBOL_GPL(filemap_maybe_emit_fsnotify_event); + /** * filemap_fault - read in file data for page fault handling * @vmf: struct vm_fault containing details of the fault @@ -3299,6 +3366,19 @@ vm_fault_t filemap_fault(struct vm_fault *vmf) if (unlikely(index >= max_idx)) return VM_FAULT_SIGBUS; + /* + * If we have pre-content watchers then we need to generate events on + * page fault so that we can populate any data before the fault. + */ + ret = filemap_maybe_emit_fsnotify_event(vmf, &fpin); + if (unlikely(ret)) { + if (fpin) { + fput(fpin); + ret |= VM_FAULT_RETRY; + } + return ret; + } + /* * Do we have something in the page cache already? */ @@ -3309,21 +3389,24 @@ vm_fault_t filemap_fault(struct vm_fault *vmf) * the lock. */ if (!(vmf->flags & FAULT_FLAG_TRIED)) - fpin = do_async_mmap_readahead(vmf, folio); + fpin = do_async_mmap_readahead(vmf, folio, fpin); if (unlikely(!folio_test_uptodate(folio))) { filemap_invalidate_lock_shared(mapping); mapping_locked = true; } } else { ret = filemap_fault_recheck_pte_none(vmf); - if (unlikely(ret)) + if (unlikely(ret)) { + if (fpin) + goto out_retry; return ret; + } /* No page in the page cache at all */ count_vm_event(PGMAJFAULT); count_memcg_event_mm(vmf->vma->vm_mm, PGMAJFAULT); ret = VM_FAULT_MAJOR; - fpin = do_sync_mmap_readahead(vmf); + fpin = do_sync_mmap_readahead(vmf, fpin); retry_find: /* * See comment in filemap_create_folio() why we need
FS_PRE_ACCESS or FS_PRE_MODIFY will be generated on page fault depending on the faulting method. This pre-content event is meant to be used by hierarchical storage managers that want to fill in the file content on first read access. Signed-off-by: Josef Bacik <josef@toxicpanda.com> --- include/linux/mm.h | 2 + mm/filemap.c | 97 ++++++++++++++++++++++++++++++++++++++++++---- 2 files changed, 92 insertions(+), 7 deletions(-)