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DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1773400079; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=F4uzVIqz7pq7OLZ2jBdjHr4kmFUvKLHY52M+cHA2QeM=; b=V+cY0BjRyCwwv+an7013A6hvA3GyXKTxVzI0c7mg6CUX4RHl0JdUtUuEibl7yaHJKANQrY sfoNtKukyd5R0qYUnFCiFxmhMBVUE3qhkBh4TFl3MaFTV1RL2OfuYZ423tSWXHrbh2SiI7 HmHqIv7Jx07xOw2GrVC1AFAIcvl9ClA= From: Usama Arif To: "Lorenzo Stoakes (Oracle)" Cc: Usama Arif , Andrew Morton , Clemens Ladisch , Arnd Bergmann , Greg Kroah-Hartman , "K . Y . Srinivasan" , Haiyang Zhang , Wei Liu , Dexuan Cui , Long Li , Alexander Shishkin , Maxime Coquelin , Alexandre Torgue , Miquel Raynal , Richard Weinberger , Vignesh Raghavendra , Bodo Stroesser , "Martin K . Petersen" , David Howells , Marc Dionne , Alexander Viro , Christian Brauner , Jan Kara , David Hildenbrand , "Liam R . Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Jann Horn , Pedro Falcato , linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-hyperv@vger.kernel.org, linux-stm32@st-md-mailman.stormreply.com, linux-arm-kernel@lists.infradead.org, linux-mtd@lists.infradead.org, linux-staging@lists.linux.dev, linux-scsi@vger.kernel.org, target-devel@vger.kernel.org, linux-afs@lists.infradead.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, Ryan Roberts Subject: Re: [PATCH 05/15] fs: afs: correctly drop reference count on mapping failure Date: Fri, 13 Mar 2026 04:07:43 -0700 Message-ID: <20260313110745.2573005-1-usama.arif@linux.dev> In-Reply-To: <4a5fa45119220b9d99ed72a36308aed01a30d2c1.1773346620.git.ljs@kernel.org> References: Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT On Thu, 12 Mar 2026 20:27:20 +0000 "Lorenzo Stoakes (Oracle)" wrote: > Commit 9d5403b1036c ("fs: convert most other generic_file_*mmap() users to > .mmap_prepare()") updated AFS to use the mmap_prepare callback in favour of > the deprecated mmap callback. > > However, it did not account for the fact that mmap_prepare can fail to map > due to an out of memory error, and thus should not be incrementing a > reference count on mmap_prepare. > > With the newly added vm_ops->mapped callback available, we can simply defer > this operation to that callback which is only invoked once the mapping is > successfully in place (but not yet visible to userspace as the mmap and VMA > write locks are held). > > Therefore add afs_mapped() to implement this callback for AFS. > > In practice the mapping allocations are 'too small to fail' so this is > something that realistically should never happen in practice (or would do > so in a case where the process is about to die anyway), but we should still > handle this. > > Signed-off-by: Lorenzo Stoakes (Oracle) > --- > fs/afs/file.c | 20 ++++++++++++++++---- > 1 file changed, 16 insertions(+), 4 deletions(-) > > diff --git a/fs/afs/file.c b/fs/afs/file.c > index f609366fd2ac..69ef86f5e274 100644 > --- a/fs/afs/file.c > +++ b/fs/afs/file.c > @@ -28,6 +28,8 @@ static ssize_t afs_file_splice_read(struct file *in, loff_t *ppos, > static void afs_vm_open(struct vm_area_struct *area); > static void afs_vm_close(struct vm_area_struct *area); > static vm_fault_t afs_vm_map_pages(struct vm_fault *vmf, pgoff_t start_pgoff, pgoff_t end_pgoff); > +static int afs_mapped(unsigned long start, unsigned long end, pgoff_t pgoff, > + const struct file *file, void **vm_private_data); > > const struct file_operations afs_file_operations = { > .open = afs_open, > @@ -61,6 +63,7 @@ const struct address_space_operations afs_file_aops = { > }; > > static const struct vm_operations_struct afs_vm_ops = { > + .mapped = afs_mapped, > .open = afs_vm_open, > .close = afs_vm_close, > .fault = filemap_fault, > @@ -500,13 +503,22 @@ static int afs_file_mmap_prepare(struct vm_area_desc *desc) > afs_add_open_mmap(vnode); Is the above afs_add_open_mmap an additional one, which could cause a reference leak? Does the above one need to be removed and only the one in afs_mapped() needs to be kept? > > ret = generic_file_mmap_prepare(desc); > - if (ret == 0) > - desc->vm_ops = &afs_vm_ops; > - else > - afs_drop_open_mmap(vnode); > + if (ret) > + return ret; > + > + desc->vm_ops = &afs_vm_ops; > return ret; > } > > +static int afs_mapped(unsigned long start, unsigned long end, pgoff_t pgoff, > + const struct file *file, void **vm_private_data) > +{ > + struct afs_vnode *vnode = AFS_FS_I(file_inode(file)); > + > + afs_add_open_mmap(vnode); > + return 0; > +} > + > static void afs_vm_open(struct vm_area_struct *vma) > { > afs_add_open_mmap(AFS_FS_I(file_inode(vma->vm_file))); > -- > 2.53.0 > >