linux-kernel - Re: [f2fs-dev] [PATCH 1/1] f2fs: allocate trace path buffer from names

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Message-ID: <ZEBE2iT/fKhnhrhg@google.com>
Date:   Wed, 19 Apr 2023 12:45:30 -0700
From:   Jaegeuk Kim <jaegeuk@...nel.org>
To:     Chao Yu <chao@...nel.org>
Cc:     wubo.oduw@...il.com, linux-kernel@...r.kernel.org,
        Wu Bo <bo.wu@...o.com>, linux-f2fs-devel@...ts.sourceforge.net
Subject: Re: [f2fs-dev] [PATCH 1/1] f2fs: allocate trace path buffer from
 names_cache

On 04/19, Jaegeuk Kim wrote:
> On 04/19, Chao Yu wrote:
> > On 2023/4/19 0:07, Jaegeuk Kim wrote:
> > > On 04/18, Chao Yu wrote:
> > > > On 2023/4/14 18:43, Wu Bo wrote:
> > > > > It would be better to use the dedicated slab to store path.
> > > > > 
> > > > > Signed-off-by: Wu Bo <bo.wu@...o.com>
> > > > > ---
> > > > >    fs/f2fs/file.c | 4 ++--
> > > > >    1 file changed, 2 insertions(+), 2 deletions(-)
> > > > > 
> > > > > diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
> > > > > index 15dabeac4690..27137873958f 100644
> > > > > --- a/fs/f2fs/file.c
> > > > > +++ b/fs/f2fs/file.c
> > > > > @@ -4361,7 +4361,7 @@ static void f2fs_trace_rw_file_path(struct kiocb *iocb, size_t count, int rw)
> > > > >    	struct inode *inode = file_inode(iocb->ki_filp);
> > > > >    	char *buf, *path;
> > > > > -	buf = f2fs_kmalloc(F2FS_I_SB(inode), PATH_MAX, GFP_KERNEL);
> > > > > +	buf = __getname();
> > > > 
> > > > How about:
> > > > 
> > > > buf = f2fs_kmem_cache_alloc(names_cachep, GFP_KERNEL, NULL, F2FS_I_SB(inode));
> > > 
> > > This looks like a hack using names_cachep?
> > 
> > names_cachep was exported in fs.h.
> 
> I think that's for __getname() in general, which doesn't indicate you can hack.
> No one is using like that.
> 
> $ grep names_cachep fs/* -R
> fs/dcache.c:struct kmem_cache *names_cachep __read_mostly;
> fs/dcache.c:EXPORT_SYMBOL(names_cachep);
> fs/dcache.c:	names_cachep = kmem_cache_create_usercopy("names_cache", PATH_MAX, 0,
> 
> $ grep __getname fs/* -R
> fs/ceph/mds_client.c:	path = __getname();
> fs/cifs/cifsproto.h:	return __getname();
> fs/dcache.c:/* SLAB cache for __getname() consumers */
> fs/d_path.c:	char *page = __getname();
> fs/exfat/dir.c:	nb->lfn = __getname();
> fs/f2fs/file.c:	buf = __getname();
> fs/fat/dir.c:		*unicode = __getname();
> fs/fat/namei_vfat.c:	uname = __getname();
> fs/hostfs/hostfs_kern.c:	char *name = __getname();
> fs/namei.c:	result = __getname();
> fs/namei.c:	result = __getname();
> fs/ntfs3/dir.c:	name = __getname();
> fs/ntfs3/xattr.c:	buf = __getname();
> fs/ntfs3/inode.c:	new_de = __getname();
> fs/ntfs3/inode.c:	de = __getname();
> fs/ntfs3/inode.c:	de = __getname();
> fs/ntfs3/namei.c:	struct cpu_str *uni = __getname();
> fs/ntfs3/namei.c:	de = __getname();
> fs/ntfs3/namei.c:	struct cpu_str *uni = __getname();
> fs/ntfs3/namei.c:	uni = __getname();
> fs/ntfs3/namei.c:	uni1 = __getname();
> fs/vboxsf/utils.c: * Returns a shfl_string allocated through __getname (must be freed using
> fs/vboxsf/utils.c:	buf = __getname();
> fs/vboxsf/utils.c:		shfl_path = __getname();
> 
> > 
> > > Using f2fs_kmem_cache_alloc is able to inject malloc error.
> > > But here is a trace event, is it ok to inject error in a trace path?
> > 
> > Yes, the fail path handling is very simple, so it's fine to leave it
> > as it is.
> > 
> > Reviewed-by: Chao Yu <chao@...nel.org>
> 
> What is this for?
> 

If we want to keep the error injection, how about this?

Signed-off-by: Wu Bo <bo.wu@...o.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@...nel.org>
---
 fs/f2fs/f2fs.h | 13 +++++++++++++
 fs/f2fs/file.c |  4 ++--
 2 files changed, 15 insertions(+), 2 deletions(-)

diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index 6cae94d51821..d87044516fe9 100644
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -3347,6 +3347,19 @@ static inline void *f2fs_kmalloc(struct f2fs_sb_info *sbi,
 	return kmalloc(size, flags);
 }
 
+static inline void *f2fs_getname(struct f2fs_sb_info *sbi)
+{
+	if (time_to_inject(sbi, FAULT_KMALLOC))
+		return NULL;
+
+	return __getname();
+}
+
+static inline void f2fs_putname(char *buf)
+{
+	__putname(buf);
+}
+
 static inline void *f2fs_kzalloc(struct f2fs_sb_info *sbi,
 					size_t size, gfp_t flags)
 {
diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
index 1b4411271f54..5ac53d2627d2 100644
--- a/fs/f2fs/file.c
+++ b/fs/f2fs/file.c
@@ -4372,7 +4372,7 @@ static void f2fs_trace_rw_file_path(struct kiocb *iocb, size_t count, int rw)
 	struct inode *inode = file_inode(iocb->ki_filp);
 	char *buf, *path;
 
-	buf = f2fs_kmalloc(F2FS_I_SB(inode), PATH_MAX, GFP_KERNEL);
+	buf = f2fs_getname(F2FS_I_SB(inode));
 	if (!buf)
 		return;
 	path = dentry_path_raw(file_dentry(iocb->ki_filp), buf, PATH_MAX);
@@ -4385,7 +4385,7 @@ static void f2fs_trace_rw_file_path(struct kiocb *iocb, size_t count, int rw)
 		trace_f2fs_dataread_start(inode, iocb->ki_pos, count,
 				current->pid, path, current->comm);
 free_buf:
-	kfree(buf);
+	f2fs_putname(buf);
 }
 
 static ssize_t f2fs_file_read_iter(struct kiocb *iocb, struct iov_iter *to)
-- 
2.40.0.634.g4ca3ef3211-goog