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The fuse file system implements > > fuse_dax_break_layouts() to do this which includes a comment > > indicating that passing dmap_end == 0 leads to unmapping of the whole > > file. > > > > However this is not true - passing dmap_end == 0 will not unmap > > anything before dmap_start, and further more > > dax_layout_busy_page_range() will not scan any of the range to see if > > there maybe ongoing DMA access to the range. > > It would be useful to clarify that this is bug was found by inspection > and that there are no known end user reports of trouble but that the > failure more would look like random fs corruption. The window is hard to > hit because a block needs to be truncated, reallocated to > a file, and written to before stale DMA could corrupt it. So that may > contribute to the fact that fuse-dax users have not reported an issue > since v5.10. > > > Fix this by checking for dmap_end == 0 in fuse_dax_break_layouts() and > > pass the entire file range to dax_layout_busy_page_range(). > > That's not what this patch does, maybe a rebase error that pushed the > @dmap_end fixup after the call to dax_layout_busy_page_range? Ha. Yep. I spotted this when doing the conversion to dax_layout_busy_page_range() and then had to rebase it into a stand alone patch for easy review. Obviously I put the check in the wrong spot, although it ends up in the right spot at the end of the series. > However, I don't think this is quite the right fix, more below... Yeah, I like your version better so will respin with that. > > Signed-off-by: Alistair Popple > > Fixes: 6ae330cad6ef ("virtiofs: serialize truncate/punch_hole and dax fault path") > > Cc: Vivek Goyal > > > > --- > > > > I am not at all familiar with the fuse file system driver so I have no > > idea if the comment is relevant or not and whether the documented > > behaviour for dmap_end == 0 is ever relied upon. However this seemed > > like the safest fix unless someone more familiar with fuse can confirm > > that dmap_end == 0 is never used. > > It is used in several places and has been wrong since day one. I believe > the original commit simply misunderstood that > dax_layout_busy_page_range() semantics are analogous to > invalidate_inode_pages2_range() semantics in terms of what @start and > @end mean. > > You can add: > > Co-developed-by: Dan Williams > Signed-off-by: Dan Williams > > ...if you end up doing a resend, or I will add it on applying to > nvdimm.git if the rebase does not end up being too prickly. Looks like I accidentally dropped a PPC fix so will do a respin for that. And the kernel build bot was complaining about incorrect documentation so will fix that while I'm at it. > -- 8< -- > diff --git a/fs/fuse/dax.c b/fs/fuse/dax.c > index c5d1feaa239c..455c4a16080b 100644 > --- a/fs/fuse/dax.c > +++ b/fs/fuse/dax.c > @@ -681,7 +681,6 @@ static int __fuse_dax_break_layouts(struct inode *inode, bool *retry, > 0, 0, fuse_wait_dax_page(inode)); > } > > -/* dmap_end == 0 leads to unmapping of whole file */ > int fuse_dax_break_layouts(struct inode *inode, u64 dmap_start, > u64 dmap_end) > { > @@ -693,10 +692,6 @@ int fuse_dax_break_layouts(struct inode *inode, u64 dmap_start, > ret = __fuse_dax_break_layouts(inode, &retry, dmap_start, > dmap_end); > } while (ret == 0 && retry); > - if (!dmap_end) { > - dmap_start = 0; > - dmap_end = LLONG_MAX; > - } > > return ret; > } > diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c > index 0b2f8567ca30..bc6c8936c529 100644 > --- a/fs/fuse/dir.c > +++ b/fs/fuse/dir.c > @@ -1936,7 +1936,7 @@ int fuse_do_setattr(struct mnt_idmap *idmap, struct dentry *dentry, > if (FUSE_IS_DAX(inode) && is_truncate) { > filemap_invalidate_lock(mapping); > fault_blocked = true; > - err = fuse_dax_break_layouts(inode, 0, 0); > + err = fuse_dax_break_layouts(inode, 0, -1); > if (err) { > filemap_invalidate_unlock(mapping); > return err; > diff --git a/fs/fuse/file.c b/fs/fuse/file.c > index 082ee374f694..cef7a8f75821 100644 > --- a/fs/fuse/file.c > +++ b/fs/fuse/file.c > @@ -253,7 +253,7 @@ static int fuse_open(struct inode *inode, struct file *file) > > if (dax_truncate) { > filemap_invalidate_lock(inode->i_mapping); > - err = fuse_dax_break_layouts(inode, 0, 0); > + err = fuse_dax_break_layouts(inode, 0, -1); > if (err) > goto out_inode_unlock; > } > @@ -2890,7 +2890,7 @@ static long fuse_file_fallocate(struct file *file, int mode, loff_t offset, > inode_lock(inode); > if (block_faults) { > filemap_invalidate_lock(inode->i_mapping); > - err = fuse_dax_break_layouts(inode, 0, 0); > + err = fuse_dax_break_layouts(inode, 0, -1); > if (err) > goto out; > }