Message ID | 20190410202115.64501-2-ebiggers@kernel.org (mailing list archive) |
---|---|
State | New, archived |
Headers | show |
Series | fscrypt: improve encrypted symlink performance | expand |
On Wed, Apr 10, 2019 at 01:21:14PM -0700, Eric Biggers wrote: > From: Eric Biggers <ebiggers@google.com> > > Use 'READ_ONCE(inode->i_link)' to explicitly support filesystems caching > the symlink target in ->i_link later if it was unavailable at iget() > time, or wasn't easily available. I'll be doing this in fscrypt, to > improve the performance of encrypted symlinks on ext4, f2fs, and ubifs. > > ->i_link will start NULL and may later be set to a non-NULL value by a > smp_store_release() or cmpxchg_release(). READ_ONCE() is needed on the > read side. smp_load_acquire() is unnecessary because only a data > dependency barrier is required. (Thanks to Al for pointing this out.) You've missed vfs_readlink()...
On Wed, Apr 10, 2019 at 10:06:57PM +0100, Al Viro wrote: > On Wed, Apr 10, 2019 at 01:21:14PM -0700, Eric Biggers wrote: > > From: Eric Biggers <ebiggers@google.com> > > > > Use 'READ_ONCE(inode->i_link)' to explicitly support filesystems caching > > the symlink target in ->i_link later if it was unavailable at iget() > > time, or wasn't easily available. I'll be doing this in fscrypt, to > > improve the performance of encrypted symlinks on ext4, f2fs, and ubifs. > > > > ->i_link will start NULL and may later be set to a non-NULL value by a > > smp_store_release() or cmpxchg_release(). READ_ONCE() is needed on the > > read side. smp_load_acquire() is unnecessary because only a data > > dependency barrier is required. (Thanks to Al for pointing this out.) > > You've missed vfs_readlink()... How so? The patch already updates vfs_readlink(). - Eric
On Wed, Apr 10, 2019 at 04:15:48PM -0700, Eric Biggers wrote: > On Wed, Apr 10, 2019 at 10:06:57PM +0100, Al Viro wrote: > > On Wed, Apr 10, 2019 at 01:21:14PM -0700, Eric Biggers wrote: > > > From: Eric Biggers <ebiggers@google.com> > > > > > > Use 'READ_ONCE(inode->i_link)' to explicitly support filesystems caching > > > the symlink target in ->i_link later if it was unavailable at iget() > > > time, or wasn't easily available. I'll be doing this in fscrypt, to > > > improve the performance of encrypted symlinks on ext4, f2fs, and ubifs. > > > > > > ->i_link will start NULL and may later be set to a non-NULL value by a > > > smp_store_release() or cmpxchg_release(). READ_ONCE() is needed on the > > > read side. smp_load_acquire() is unnecessary because only a data > > > dependency barrier is required. (Thanks to Al for pointing this out.) > > > > You've missed vfs_readlink()... > > How so? The patch already updates vfs_readlink(). Huh? Right you are - fsck knows how have I managed to misread that... Anyway, I can pick that READ_ONCE() patch through vfs.git if you wish, or it can go through your tree with my Acked-by - up to you...
On Thu, Apr 11, 2019 at 03:25:15AM +0100, Al Viro wrote: > On Wed, Apr 10, 2019 at 04:15:48PM -0700, Eric Biggers wrote: > > On Wed, Apr 10, 2019 at 10:06:57PM +0100, Al Viro wrote: > > > On Wed, Apr 10, 2019 at 01:21:14PM -0700, Eric Biggers wrote: > > > > From: Eric Biggers <ebiggers@google.com> > > > > > > > > Use 'READ_ONCE(inode->i_link)' to explicitly support filesystems caching > > > > the symlink target in ->i_link later if it was unavailable at iget() > > > > time, or wasn't easily available. I'll be doing this in fscrypt, to > > > > improve the performance of encrypted symlinks on ext4, f2fs, and ubifs. > > > > > > > > ->i_link will start NULL and may later be set to a non-NULL value by a > > > > smp_store_release() or cmpxchg_release(). READ_ONCE() is needed on the > > > > read side. smp_load_acquire() is unnecessary because only a data > > > > dependency barrier is required. (Thanks to Al for pointing this out.) > > > > > > You've missed vfs_readlink()... > > > > How so? The patch already updates vfs_readlink(). > > Huh? Right you are - fsck knows how have I managed to misread that... > Anyway, I can pick that READ_ONCE() patch through vfs.git if you wish, > or it can go through your tree with my Acked-by - up to you... Unless you expect merge conflicts, it's easier for me to take it through the fscrypt tree, since it's a small patch and the second patch technically isn't correct without it. I'll add your Acked-by. Are you planning to review the second patch too? Thanks! - Eric
On Thu, Apr 11, 2019 at 03:25:15AM +0100, Al Viro wrote: > On Wed, Apr 10, 2019 at 04:15:48PM -0700, Eric Biggers wrote: > > On Wed, Apr 10, 2019 at 10:06:57PM +0100, Al Viro wrote: > > > On Wed, Apr 10, 2019 at 01:21:14PM -0700, Eric Biggers wrote: > > > > From: Eric Biggers <ebiggers@google.com> > > > > > > > > Use 'READ_ONCE(inode->i_link)' to explicitly support filesystems caching > > > > the symlink target in ->i_link later if it was unavailable at iget() > > > > time, or wasn't easily available. I'll be doing this in fscrypt, to > > > > improve the performance of encrypted symlinks on ext4, f2fs, and ubifs. > > > > > > > > ->i_link will start NULL and may later be set to a non-NULL value by a > > > > smp_store_release() or cmpxchg_release(). READ_ONCE() is needed on the > > > > read side. smp_load_acquire() is unnecessary because only a data > > > > dependency barrier is required. (Thanks to Al for pointing this out.) > > > > > > You've missed vfs_readlink()... > > > > How so? The patch already updates vfs_readlink(). > > Huh? Right you are - fsck knows how have I managed to misread that... > Anyway, I can pick that READ_ONCE() patch through vfs.git if you wish, > or it can go through your tree with my Acked-by - up to you... Al, I'll take it through the fscrypt tree with your Acked-by, if you don't mind. - Ted
diff --git a/fs/namei.c b/fs/namei.c index dede0147b3f6e..2855de004c1a9 100644 --- a/fs/namei.c +++ b/fs/namei.c @@ -1066,7 +1066,7 @@ const char *get_link(struct nameidata *nd) return ERR_PTR(error); nd->last_type = LAST_BIND; - res = inode->i_link; + res = READ_ONCE(inode->i_link); if (!res) { const char * (*get)(struct dentry *, struct inode *, struct delayed_call *); @@ -4729,7 +4729,7 @@ int vfs_readlink(struct dentry *dentry, char __user *buffer, int buflen) spin_unlock(&inode->i_lock); } - link = inode->i_link; + link = READ_ONCE(inode->i_link); if (!link) { link = inode->i_op->get_link(dentry, inode, &done); if (IS_ERR(link))