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Wed, 13 Aug 2025 12:50:53 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id pOLiIy2KnGhIUQAAD6G6ig (envelope-from ); Wed, 13 Aug 2025 12:50:53 +0000 Date: Wed, 13 Aug 2025 14:50:52 +0200 From: David Sterba To: Leo Martins Cc: linux-btrfs@vger.kernel.org, kernel-team@fb.com Subject: Re: [PATCH v4 1/3] btrfs: implement ref_tracker for delayed_nodes Message-ID: <20250813125052.GC22430@twin.jikos.cz> Reply-To: dsterba@suse.cz References: Precedence: bulk X-Mailing-List: linux-btrfs@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.23.1-rc1 (2014-03-12) X-Spamd-Result: default: False [-4.21 / 50.00]; BAYES_HAM(-3.00)[100.00%]; NEURAL_HAM_LONG(-1.00)[-1.000]; HAS_REPLYTO(0.30)[dsterba@suse.cz]; R_DKIM_ALLOW(-0.20)[suse.cz:s=susede2_rsa,suse.cz:s=susede2_ed25519]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; MX_GOOD(-0.01)[]; FREEMAIL_ENVRCPT(0.00)[gmail.com]; DKIM_SIGNED(0.00)[suse.cz:s=susede2_rsa,suse.cz:s=susede2_ed25519]; FREEMAIL_TO(0.00)[gmail.com]; RBL_SPAMHAUS_BLOCKED_OPENRESOLVER(0.00)[2a07:de40:b281:104:10:150:64:97:from]; ARC_NA(0.00)[]; SPAMHAUS_XBL(0.00)[2a07:de40:b281:104:10:150:64:97:from]; FUZZY_RATELIMITED(0.00)[rspamd.com]; TO_DN_SOME(0.00)[]; MIME_TRACE(0.00)[0:+]; TO_MATCH_ENVRCPT_ALL(0.00)[]; RCVD_TLS_ALL(0.00)[]; REPLYTO_DOM_NEQ_TO_DOM(0.00)[]; REPLYTO_ADDR_EQ_FROM(0.00)[]; FROM_EQ_ENVFROM(0.00)[]; FROM_HAS_DN(0.00)[]; DKIM_TRACE(0.00)[suse.cz:+]; RCVD_COUNT_TWO(0.00)[2]; TAGGED_RCPT(0.00)[]; RECEIVED_SPAMHAUS_BLOCKED_OPENRESOLVER(0.00)[2a07:de40:b281:106:10:150:64:167:received]; RCPT_COUNT_THREE(0.00)[3]; RCVD_VIA_SMTP_AUTH(0.00)[]; DBL_BLOCKED_OPENRESOLVER(0.00)[imap1.dmz-prg2.suse.org:helo,imap1.dmz-prg2.suse.org:rdns] X-Spam-Flag: NO X-Spam-Level: X-Rspamd-Queue-Id: ADADA21271 X-Rspamd-Server: rspamd2.dmz-prg2.suse.org X-Rspamd-Action: no action X-Spam-Score: -4.21 On Tue, Aug 12, 2025 at 04:04:39PM -0700, Leo Martins wrote: > This patch adds ref_tracker infrastructure for btrfs_delayed_node. > > It is a response to the largest btrfs related crash in our fleet. > We're seeing softlockups in btrfs_kill_all_delayed_nodes that seem > to be a result of delayed_nodes not being released properly. > > A ref_tracker object is allocated on reference count increases and > freed on reference count decreases. The ref_tracker object stores > a stack trace of where it is allocated. The ref_tracker_dir object > is embedded in btrfs_delayed_node and keeps track of all current > and some old/freed ref_tracker objects. When a leak is detected > we can print the stack traces for all ref_trackers that have not > yet been freed. > > Here is a common example of taking a reference to a delayed_node > and freeing it with ref_tracker. > > ```C > struct btrfs_ref_tracker tracker; > struct btrfs_delayed_node *node; > > node = btrfs_get_delayed_node(inode, &tracker); > // use delayed_node... > btrfs_release_delayed_node(node, &tracker); > ``` > > There are two special cases where the delayed_node reference is "long > lived", meaning that the thread that takes the reference and the thread > that releases the reference are different. The `inode_cache_tracker` > tracks the delayed_node stored in btrfs_inode. The `node_list_tracker` > tracks the delayed_node stored in the btrfs_delayed_root > node_list/prepare_list. These trackers are embedded in the > btrfs_delayed_node. > > btrfs_ref_tracker and btrfs_ref_tracker_dir are wrappers that either > compile to the corresponding ref_tracker structs or empty structs > depending on CONFIG_BTRFS_DEBUG. There are also btrfs wrappers for > the ref_tracker API. > > Signed-off-by: Leo Martins There's some witespace damage that fails when the patch is applied by 'git am', it can be fixed manually but please fix that next time. > --- > fs/btrfs/Kconfig | 3 +- > fs/btrfs/delayed-inode.c | 192 ++++++++++++++++++++++++++++----------- > fs/btrfs/delayed-inode.h | 70 ++++++++++++++ > 3 files changed, 209 insertions(+), 56 deletions(-) > > diff --git a/fs/btrfs/Kconfig b/fs/btrfs/Kconfig > index c352f3ae0385..2745de514196 100644 > --- a/fs/btrfs/Kconfig > +++ b/fs/btrfs/Kconfig > @@ -61,7 +61,8 @@ config BTRFS_FS_RUN_SANITY_TESTS > > config BTRFS_DEBUG > bool "Btrfs debugging support" > - depends on BTRFS_FS > + depends on BTRFS_FS && STACKTRACE_SUPPORT How does this work? If STACKTRACE_SUPPORT is not enabled then we can't enable BTRFS_DEBUG? > + select REF_TRACKER > help > Enable run-time debugging support for the btrfs filesystem. > > @@ -78,6 +95,12 @@ struct btrfs_delayed_node { > * actual number of leaves we end up using. Protected by @mutex. > */ > u32 index_item_leaves; > + /* Used to track all references to this delayed node. */ > + struct btrfs_ref_tracker_dir ref_dir; > + /* Used to track delayed node reference stored in node list. */ > + struct btrfs_ref_tracker node_list_tracker; > + /* Used to track delayed node reference stored in inode cache. */ > + struct btrfs_ref_tracker inode_cache_tracker; Some of the comments have mixed space and tabs in the initial space. > }; > > struct btrfs_delayed_item { > @@ -169,4 +192,51 @@ void __cold btrfs_delayed_inode_exit(void); > /* for debugging */ > void btrfs_assert_delayed_root_empty(struct btrfs_fs_info *fs_info); > > +#define BTRFS_DELAYED_NODE_REF_TRACKER_QUARANTINE_COUNT 16 > +#define BTRFS_DELAYED_NODE_REF_TRACKER_DISPLAY_LIMIT 16 > + > +#ifdef CONFIG_BTRFS_DEBUG > +static inline void btrfs_delayed_node_ref_tracker_dir_init(struct btrfs_delayed_node *node) > +{ > + ref_tracker_dir_init(&node->ref_dir.dir, Trailing space. > + BTRFS_DELAYED_NODE_REF_TRACKER_QUARANTINE_COUNT, > + "delayed_node"); > +}