From patchwork Sat Feb 17 20:23:40 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Chuck Lever X-Patchwork-Id: 13561578 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 9F6DC7F48B; Sat, 17 Feb 2024 20:23:42 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1708201422; cv=none; b=OPCVtslzwYeUx0LNhhbZ+xx97T07EOaZWxcQzjb4C9X6X/t+qEQBRncuuMge1Ed4r5l8aa1ZdWU2i/VO2mHpQOkdZd7g7HVtNJN8jB7CdldziP7VTt43AJtHXDIgiE19rGX5YmjVOYdTtCiET/PSbzcq8LoCsW8tjDkQ0zA06Ik= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1708201422; c=relaxed/simple; bh=R5X4D36CuE1wpCsrFE/3Fuex0DnO2GtnjfkqVv5cjQg=; h=Subject:From:To:Cc:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=BzUEFfjFPuZ4aoi9hVC7uDl1OA6ZiB7JI7Kq1Qy9L2bjt/iHE06/moj1rpQppUAJUSpiwb3YO1F9SdGdpH7KPhJTTdoRU+gxk417zW5XEqClsIFHldXRi7aae1KuxNvr+2aDrOFAdVDUkrqobXpOZbzt/y1P3e0RSfotP8lYOHQ= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=P4X30OxK; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="P4X30OxK" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 32618C433F1; Sat, 17 Feb 2024 20:23:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1708201422; bh=R5X4D36CuE1wpCsrFE/3Fuex0DnO2GtnjfkqVv5cjQg=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=P4X30OxKc0EN8nPXm8GE/AdSc3yeT5iVNwWMRGyRMVcJFIie5F4caTrhUc28NAuXO 9voVKSq/opp81jg2cRH3/szMzpTTQ/4XgrT8WdD2WpFkvBWhxoEj1F/vcTYv1kOP4+ FZdDrkL9Ov1gk0qvcx9T66jKl6xWpHB0h4rQB5Ze7WhCUX3SKZ6cEUOGk9Z5vnO5+j XY0aze0RMR8AG9xJitjPfN95aBR+joD0NoDr2zyACqqmGYNchunmvsmDUeW9cgCf9a DCi8QemiRpOkaILmDK6aiHQNcv88w0pNMBL71uYhHVosom/O2z6gP7OwvFkgLUc3ph MCA7wONlVDoYw== Subject: [PATCH v2 1/6] libfs: Re-arrange locking in offset_iterate_dir() From: Chuck Lever To: viro@zeniv.linux.org.uk, brauner@kernel.org, jack@suse.cz, hughd@google.com, akpm@linux-foundation.org, Liam.Howlett@oracle.com, oliver.sang@intel.com, feng.tang@intel.com Cc: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, maple-tree@lists.infradead.org, linux-mm@kvack.org, lkp@intel.com Date: Sat, 17 Feb 2024 15:23:40 -0500 Message-ID: <170820142021.6328.15047865406275957018.stgit@91.116.238.104.host.secureserver.net> In-Reply-To: <170820083431.6328.16233178852085891453.stgit@91.116.238.104.host.secureserver.net> References: <170820083431.6328.16233178852085891453.stgit@91.116.238.104.host.secureserver.net> User-Agent: StGit/1.5 Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 From: Chuck Lever Liam and Matthew say that once the RCU read lock is released, xa_state is not safe to re-use for the next xas_find() call. But the RCU read lock must be released on each loop iteration so that dput(), which might_sleep(), can be called safely. Thus we are forced to walk the offset tree with fresh state for each directory entry. xa_find() can do this for us, though it might be a little less efficient than maintaining xa_state locally. We believe that in the current code base, inode->i_rwsem provides protection for the xa_state maintained in offset_iterate_dir(). However, there is no guarantee that will continue to be the case in the future. Since offset_iterate_dir() doesn't build xa_state locally any more, there's no longer a strong need for offset_find_next(). Clean up by rolling these two helpers together. Suggested-by: Liam R. Howlett Message-ID: <170785993027.11135.8830043889278631735.stgit@91.116.238.104.host.secureserver.net> Signed-off-by: Chuck Lever Reviewed-by: Jan Kara --- fs/libfs.c | 12 ++++++------ 1 file changed, 6 insertions(+), 6 deletions(-) diff --git a/fs/libfs.c b/fs/libfs.c index eec6031b0155..752e24c669d9 100644 --- a/fs/libfs.c +++ b/fs/libfs.c @@ -402,12 +402,13 @@ static loff_t offset_dir_llseek(struct file *file, loff_t offset, int whence) return vfs_setpos(file, offset, U32_MAX); } -static struct dentry *offset_find_next(struct xa_state *xas) +static struct dentry *offset_find_next(struct offset_ctx *octx, loff_t offset) { struct dentry *child, *found = NULL; + XA_STATE(xas, &octx->xa, offset); rcu_read_lock(); - child = xas_next_entry(xas, U32_MAX); + child = xas_next_entry(&xas, U32_MAX); if (!child) goto out; spin_lock(&child->d_lock); @@ -430,12 +431,11 @@ static bool offset_dir_emit(struct dir_context *ctx, struct dentry *dentry) static void *offset_iterate_dir(struct inode *inode, struct dir_context *ctx) { - struct offset_ctx *so_ctx = inode->i_op->get_offset_ctx(inode); - XA_STATE(xas, &so_ctx->xa, ctx->pos); + struct offset_ctx *octx = inode->i_op->get_offset_ctx(inode); struct dentry *dentry; while (true) { - dentry = offset_find_next(&xas); + dentry = offset_find_next(octx, ctx->pos); if (!dentry) return ERR_PTR(-ENOENT); @@ -444,8 +444,8 @@ static void *offset_iterate_dir(struct inode *inode, struct dir_context *ctx) break; } + ctx->pos = dentry2offset(dentry) + 1; dput(dentry); - ctx->pos = xas.xa_index + 1; } return NULL; }