Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755546AbbHNRVz (ORCPT ); Fri, 14 Aug 2015 13:21:55 -0400 Received: from mx1.redhat.com ([209.132.183.28]:57216 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755352AbbHNRVx (ORCPT ); Fri, 14 Aug 2015 13:21:53 -0400 Date: Fri, 14 Aug 2015 19:19:35 +0200 From: Oleg Nesterov To: Al Viro Cc: Dave Chinner , Dave Hansen , Jan Kara , "Paul E. McKenney" , Peter Zijlstra , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH v3 0/8] change sb_writers to use percpu_rw_semaphore Message-ID: <20150814171935.GA15042@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4532 Lines: 134 On 08/13, Jan Kara wrote: > > Regarding the routing, ideally Al Viro should take these as a VFS > maintainer. Al, could you take these patches? Only cosmetic changes in V3 to address the comments from Jan, I preserved his acks. In case you missed all the spam I sent before, let me repeat that the awful (and currently unneeded) 7/8 will be reverted later. We need it to ensure that other percpu_rw_semaphore changes routed via another tree won't break fs/super.c. After that we will add rcu_sync_dtor(s_writers->rw_sem) into deactivate_locked_super() and revert this horror. 3/8 documents the lockdep problems we currently have. This is fixed by the patch below but it depends on xfs ILOCK fixes from Dave, so I will send it later. Plus another patch which removes the "trylock" hack in __sb_start_write(). Oleg. arch/Kconfig | 1 - fs/btrfs/transaction.c | 8 +-- fs/super.c | 184 +++++++++++++++++++--------------------- fs/xfs/xfs_aops.c | 6 +- include/linux/fs.h | 23 +++--- include/linux/percpu-rwsem.h | 20 +++++ init/Kconfig | 1 - kernel/locking/Makefile | 3 +- kernel/locking/percpu-rwsem.c | 13 +++ lib/Kconfig | 3 - 10 files changed, 136 insertions(+), 126 deletions(-) -------------------------------------------------------------------------- [PATCH v3 9/8] don't fool lockdep in freeze_super() and thaw_super() paths sb_wait_write()->percpu_rwsem_release() fools lockdep to avoid the false-positives. Now that xfs was fixed by Dave we can remove it and change freeze_super() and thaw_super() to run with s_writers.rw_sem locks held; we add two trivial helpers for that, sb_freeze_release() and sb_freeze_acquire(). Signed-off-by: Oleg Nesterov Reviewed-by: Jan Kara --- fs/super.c | 37 +++++++++++++++++++++++++------------ 1 files changed, 25 insertions(+), 12 deletions(-) diff --git a/fs/super.c b/fs/super.c index 4350ff4..91c9756 100644 --- a/fs/super.c +++ b/fs/super.c @@ -1213,25 +1213,34 @@ EXPORT_SYMBOL(__sb_start_write); static void sb_wait_write(struct super_block *sb, int level) { percpu_down_write(sb->s_writers.rw_sem + level-1); - /* - * We are going to return to userspace and forget about this lock, the - * ownership goes to the caller of thaw_super() which does unlock. - * - * FIXME: we should do this before return from freeze_super() after we - * called sync_filesystem(sb) and s_op->freeze_fs(sb), and thaw_super() - * should re-acquire these locks before s_op->unfreeze_fs(sb). However - * this leads to lockdep false-positives, so currently we do the early - * release right after acquire. - */ - percpu_rwsem_release(sb->s_writers.rw_sem + level-1, 0, _THIS_IP_); } -static void sb_freeze_unlock(struct super_block *sb) +/* + * We are going to return to userspace and forget about these locks, the + * ownership goes to the caller of thaw_super() which does unlock(). + */ +static void sb_freeze_release(struct super_block *sb) +{ + int level; + + for (level = SB_FREEZE_LEVELS - 1; level >= 0; level--) + percpu_rwsem_release(sb->s_writers.rw_sem + level, 0, _THIS_IP_); +} + +/* + * Tell lockdep we are holding these locks before we call ->unfreeze_fs(sb). + */ +static void sb_freeze_acquire(struct super_block *sb) { int level; for (level = 0; level < SB_FREEZE_LEVELS; ++level) percpu_rwsem_acquire(sb->s_writers.rw_sem + level, 0, _THIS_IP_); +} + +static void sb_freeze_unlock(struct super_block *sb) +{ + int level; for (level = SB_FREEZE_LEVELS - 1; level >= 0; level--) percpu_up_write(sb->s_writers.rw_sem + level); @@ -1327,6 +1336,7 @@ int freeze_super(struct super_block *sb) * sees write activity when frozen is set to SB_FREEZE_COMPLETE. */ sb->s_writers.frozen = SB_FREEZE_COMPLETE; + sb_freeze_release(sb); up_write(&sb->s_umount); return 0; } @@ -1353,11 +1363,14 @@ int thaw_super(struct super_block *sb) goto out; } + sb_freeze_acquire(sb); + if (sb->s_op->unfreeze_fs) { error = sb->s_op->unfreeze_fs(sb); if (error) { printk(KERN_ERR "VFS:Filesystem thaw failed\n"); + sb_freeze_release(sb); up_write(&sb->s_umount); return error; } -- 1.5.5.1 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/