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Use d_find_any_alias() and no longer hold i_lock. Signed-off-by: Stephen Brennan Reviewed-by: Amir Goldstein --- fs/notify/fsnotify.c | 41 ++++++++++++++++++----------------------- 1 file changed, 18 insertions(+), 23 deletions(-) diff --git a/fs/notify/fsnotify.c b/fs/notify/fsnotify.c index 7974e91ffe13..6c338322f0c3 100644 --- a/fs/notify/fsnotify.c +++ b/fs/notify/fsnotify.c @@ -105,7 +105,7 @@ void fsnotify_sb_delete(struct super_block *sb) */ void __fsnotify_update_child_dentry_flags(struct inode *inode) { - struct dentry *alias; + struct dentry *alias, *child; int watched; if (!S_ISDIR(inode->i_mode)) @@ -114,30 +114,25 @@ void __fsnotify_update_child_dentry_flags(struct inode *inode) /* determine if the children should tell inode about their events */ watched = fsnotify_inode_watches_children(inode); - spin_lock(&inode->i_lock); - /* run all of the dentries associated with this inode. Since this is a - * directory, there damn well better only be one item on this list */ - hlist_for_each_entry(alias, &inode->i_dentry, d_u.d_alias) { - struct dentry *child; - - /* run all of the children of the original inode and fix their - * d_flags to indicate parental interest (their parent is the - * original inode) */ - spin_lock(&alias->d_lock); - list_for_each_entry(child, &alias->d_subdirs, d_child) { - if (!child->d_inode) - continue; + /* Since this is a directory, there damn well better only be one child */ + alias = d_find_any_alias(inode); - spin_lock_nested(&child->d_lock, DENTRY_D_LOCK_NESTED); - if (watched) - child->d_flags |= DCACHE_FSNOTIFY_PARENT_WATCHED; - else - child->d_flags &= ~DCACHE_FSNOTIFY_PARENT_WATCHED; - spin_unlock(&child->d_lock); - } - spin_unlock(&alias->d_lock); + /* run all of the children of the original inode and fix their + * d_flags to indicate parental interest (their parent is the + * original inode) */ + spin_lock(&alias->d_lock); + list_for_each_entry(child, &alias->d_subdirs, d_child) { + if (!child->d_inode) + continue; + + spin_lock_nested(&child->d_lock, DENTRY_D_LOCK_NESTED); + if (watched) + child->d_flags |= DCACHE_FSNOTIFY_PARENT_WATCHED; + else + child->d_flags &= ~DCACHE_FSNOTIFY_PARENT_WATCHED; + spin_unlock(&child->d_lock); } - spin_unlock(&inode->i_lock); + spin_unlock(&alias->d_lock); } /* Are inode/sb/mount interested in parent and name info with this event? */ From patchwork Fri Oct 21 01:03:09 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Stephen Brennan X-Patchwork-Id: 6464 Return-Path: Delivered-To: ouuuleilei@gmail.com Received: by 2002:a5d:4242:0:0:0:0:0 with SMTP id s2csp411356wrr; Thu, 20 Oct 2022 18:11:19 -0700 (PDT) X-Google-Smtp-Source: AMsMyM6tOTkAReSNV0W381g8Z6W4UDa9c6P0t66phLmGrwhZ9ET9jxA31qmGDAXLNEXY6b4uQ+Gq X-Received: by 2002:a05:6402:1e88:b0:45d:237f:f468 with SMTP id f8-20020a0564021e8800b0045d237ff468mr14495211edf.45.1666314679264; Thu, 20 Oct 2022 18:11:19 -0700 (PDT) ARC-Seal: i=2; a=rsa-sha256; t=1666314679; cv=pass; d=google.com; s=arc-20160816; b=OtbHKc5NHdHD2DWQhDf39DlSidVpWxNlmc09UEsqpFD6av+oyMT/EYltuYXusYDO0X bEVXKcNgb76CG9sD38JgdrkdlyRcKQqbwz2FZrVtYJHV8cfvC2S/s6nNHnM8vdehDDIa 8I/dzxuojBxDl3OerHF3UAnjL36vprJa8h5C6jKu9NWyBc1TWosXimVYMPsx2LG6gjjJ 2D+EUcbygAj281A7IJpAX1x3+1Tdi6fp3as6k5ZuSRKXFXDcysI4FQc7t96yPWHF9q4l ATYJXpkJKl7LUtqcxNydHAXpK2I5LGYVThEZqZwzjOQdSzJRKmOvQP1xvQnYfSvqpbIo N5sA== ARC-Message-Signature: i=2; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=list-id:precedence:mime-version:content-transfer-encoding :references:in-reply-to:message-id:date:subject:cc:to:from :dkim-signature:dkim-signature; bh=0WOghY6ZIKv7cRpCv/K161JkS/g/KW77oLuKKhjFVco=; b=XMD6qM5D338Rjsoc0yPKwcr1Qg9ME7rlS6100osgLOR/z+PLC8Lr5oD289JdV1FQhK 1pvEUXJ/u72Sp1sS2zch4mYEa/vDOIcWXcCOtJ13a/YDZb5j811TsFjlvkFoXPgA8sie AXw1+2HinEDF0F2qBEkhP/5e/nCYes9AncVagOZMxHeJ/UFHMbM/wNQ7IjIruO2qxKkS u47KhLgVxQMPGC97COBT66vqbRrqBTtmLVwky241aunBW9gQq4lk6XivLqgSAscDH4sg 7c1lu6rb1vC+pWx0do9EY49gLQTybhVkdcov8gHBeLsVkdnRApjhMeTx/6GvPQLeqDzs rlFQ== ARC-Authentication-Results: i=2; mx.google.com; dkim=pass header.i=@oracle.com header.s=corp-2022-7-12 header.b=kCj17FdM; dkim=pass header.i=@oracle.onmicrosoft.com header.s=selector2-oracle-onmicrosoft-com header.b=siBR6jTb; arc=pass (i=1 spf=pass spfdomain=oracle.com dkim=pass dkdomain=oracle.com dmarc=pass fromdomain=oracle.com); spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=oracle.com Received: from out1.vger.email (out1.vger.email. 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Currently, when the fsnotify connector is removed and i_fsnotify_mask becomes zero, we lazily allow __fsnotify_parent() to do this the next time we see an event on a child. However, if the list of children is very long (e.g., in the millions), and lots of activity is occurring on the directory, then it's possible for many CPUs to end up blocked on the inode spinlock in __fsnotify_update_child_flags(). Each CPU will then redundantly iterate over the very long list of children. This situation can cause soft lockups. To avoid this, stop lazily updating child flags in __fsnotify_parent(). Instead, update flags when we disconnect a mark connector. Remember the state of the children flags in the fsnotify_mark_connector flags. Provide mutual exclusion by holding i_rwsem exclusive while we update children, and use the cached state to avoid updating flags unnecessarily. Signed-off-by: Stephen Brennan --- fs/notify/fsnotify.c | 22 ++++++- fs/notify/fsnotify.h | 31 ++++++++- fs/notify/mark.c | 106 ++++++++++++++++++++----------- include/linux/fsnotify_backend.h | 8 +++ 4 files changed, 127 insertions(+), 40 deletions(-) diff --git a/fs/notify/fsnotify.c b/fs/notify/fsnotify.c index 6c338322f0c3..f83eca4fb841 100644 --- a/fs/notify/fsnotify.c +++ b/fs/notify/fsnotify.c @@ -103,13 +103,15 @@ void fsnotify_sb_delete(struct super_block *sb) * parent cares. Thus when an event happens on a child it can quickly tell * if there is a need to find a parent and send the event to the parent. */ -void __fsnotify_update_child_dentry_flags(struct inode *inode) +bool __fsnotify_update_children_dentry_flags(struct inode *inode) { struct dentry *alias, *child; int watched; if (!S_ISDIR(inode->i_mode)) - return; + return false; + + lockdep_assert_held_write(&inode->i_rwsem); /* determine if the children should tell inode about their events */ watched = fsnotify_inode_watches_children(inode); @@ -133,6 +135,20 @@ void __fsnotify_update_child_dentry_flags(struct inode *inode) spin_unlock(&child->d_lock); } spin_unlock(&alias->d_lock); + return watched; +} + +void __fsnotify_update_child_dentry_flags(struct inode *inode, struct dentry *dentry) +{ + /* + * Flag would be cleared soon by + * __fsnotify_update_child_dentry_flags(), but as an + * optimization, clear it now. + */ + spin_lock(&dentry->d_lock); + if (!fsnotify_inode_watches_children(inode)) + dentry->d_flags &= ~DCACHE_FSNOTIFY_PARENT_WATCHED; + spin_unlock(&dentry->d_lock); } /* Are inode/sb/mount interested in parent and name info with this event? */ @@ -203,7 +219,7 @@ int __fsnotify_parent(struct dentry *dentry, __u32 mask, const void *data, p_inode = parent->d_inode; p_mask = fsnotify_inode_watches_children(p_inode); if (unlikely(parent_watched && !p_mask)) - __fsnotify_update_child_dentry_flags(p_inode); + __fsnotify_update_child_dentry_flags(p_inode, dentry); /* * Include parent/name in notification either if some notification diff --git a/fs/notify/fsnotify.h b/fs/notify/fsnotify.h index fde74eb333cc..182d93014c6b 100644 --- a/fs/notify/fsnotify.h +++ b/fs/notify/fsnotify.h @@ -70,11 +70,40 @@ static inline void fsnotify_clear_marks_by_sb(struct super_block *sb) fsnotify_destroy_marks(&sb->s_fsnotify_marks); } +static inline bool fsnotify_children_need_update(struct fsnotify_mark_connector *conn, + struct inode *inode) +{ + bool watched, flags_set; + watched = fsnotify_inode_watches_children(inode); + flags_set = conn->flags & FSNOTIFY_CONN_FLAG_WATCHES_CHILDREN; + return (watched && !flags_set) || (!watched && flags_set); +} + /* * update the dentry->d_flags of all of inode's children to indicate if inode cares * about events that happen to its children. */ -extern void __fsnotify_update_child_dentry_flags(struct inode *inode); +extern bool __fsnotify_update_children_dentry_flags(struct inode *inode); + +static inline void fsnotify_update_children_dentry_flags(struct fsnotify_mark_connector *conn, + struct inode *inode) +{ + bool need_update; + inode_lock(inode); + spin_lock(&conn->lock); + need_update = fsnotify_children_need_update(conn, inode); + spin_unlock(&conn->lock); + if (need_update) { + bool watched = __fsnotify_update_children_dentry_flags(inode); + spin_lock(&conn->lock); + if (watched) + conn->flags |= FSNOTIFY_CONN_FLAG_WATCHES_CHILDREN; + else + conn->flags &= ~FSNOTIFY_CONN_FLAG_WATCHES_CHILDREN; + spin_unlock(&conn->lock); + } + inode_unlock(inode); +} extern struct kmem_cache *fsnotify_mark_connector_cachep; diff --git a/fs/notify/mark.c b/fs/notify/mark.c index c74ef947447d..ecfd355a93f2 100644 --- a/fs/notify/mark.c +++ b/fs/notify/mark.c @@ -130,30 +130,39 @@ static void fsnotify_get_inode_ref(struct inode *inode) * iput() outside of spinlocks. This happens when last mark that wanted iref is * detached. */ -static struct inode *fsnotify_update_iref(struct fsnotify_mark_connector *conn, - bool want_iref) +static struct inode *fsnotify_update_inode_conn_flags(struct fsnotify_mark_connector *conn, + bool want_iref, int *flags) { bool has_iref = conn->flags & FSNOTIFY_CONN_FLAG_HAS_IREF; - struct inode *inode = NULL; + struct inode *inode = NULL, *ret = NULL; - if (conn->type != FSNOTIFY_OBJ_TYPE_INODE || - want_iref == has_iref) + if (conn->type != FSNOTIFY_OBJ_TYPE_INODE) return NULL; - if (want_iref) { - /* Pin inode if any mark wants inode refcount held */ - fsnotify_get_inode_ref(fsnotify_conn_inode(conn)); - conn->flags |= FSNOTIFY_CONN_FLAG_HAS_IREF; - } else { - /* Unpin inode after detach of last mark that wanted iref */ - inode = fsnotify_conn_inode(conn); - conn->flags &= ~FSNOTIFY_CONN_FLAG_HAS_IREF; + inode = fsnotify_conn_inode(conn); + + if (want_iref != has_iref) { + if (want_iref) { + /* Pin inode if any mark wants inode refcount held */ + fsnotify_get_inode_ref(inode); + conn->flags |= FSNOTIFY_CONN_FLAG_HAS_IREF; + } else { + /* Unpin inode after detach of last mark that wanted iref */ + conn->flags &= ~FSNOTIFY_CONN_FLAG_HAS_IREF; + ret = inode; + *flags |= FSNOTIFY_OBJ_FLAG_NEED_IPUT; + } + } + if (fsnotify_children_need_update(conn, inode)) { + ret = inode; + *flags |= FSNOTIFY_OBJ_FLAG_UPDATE_CHILDREN; } - return inode; + return ret; } -static void *__fsnotify_recalc_mask(struct fsnotify_mark_connector *conn) +static void *__fsnotify_recalc_mask(struct fsnotify_mark_connector *conn, + int *flags) { u32 new_mask = 0; bool want_iref = false; @@ -173,7 +182,7 @@ static void *__fsnotify_recalc_mask(struct fsnotify_mark_connector *conn) } *fsnotify_conn_mask_p(conn) = new_mask; - return fsnotify_update_iref(conn, want_iref); + return fsnotify_update_inode_conn_flags(conn, want_iref, flags); } /* @@ -184,15 +193,19 @@ static void *__fsnotify_recalc_mask(struct fsnotify_mark_connector *conn) */ void fsnotify_recalc_mask(struct fsnotify_mark_connector *conn) { + struct inode *inode = NULL; + int flags = 0; + if (!conn) return; spin_lock(&conn->lock); - __fsnotify_recalc_mask(conn); + inode = __fsnotify_recalc_mask(conn, &flags); spin_unlock(&conn->lock); - if (conn->type == FSNOTIFY_OBJ_TYPE_INODE) - __fsnotify_update_child_dentry_flags( - fsnotify_conn_inode(conn)); + + if (flags & FSNOTIFY_OBJ_FLAG_UPDATE_CHILDREN) + fsnotify_update_children_dentry_flags(conn, inode); + WARN_ON_ONCE(flags & FSNOTIFY_OBJ_FLAG_NEED_IPUT); } /* Free all connectors queued for freeing once SRCU period ends */ @@ -240,7 +253,8 @@ static void fsnotify_put_sb_connectors(struct fsnotify_mark_connector *conn) static void *fsnotify_detach_connector_from_object( struct fsnotify_mark_connector *conn, - unsigned int *type) + unsigned int *type, + unsigned int *flags) { struct inode *inode = NULL; @@ -252,8 +266,11 @@ static void *fsnotify_detach_connector_from_object( inode = fsnotify_conn_inode(conn); inode->i_fsnotify_mask = 0; - /* Unpin inode when detaching from connector */ - if (!(conn->flags & FSNOTIFY_CONN_FLAG_HAS_IREF)) + if (conn->flags & FSNOTIFY_CONN_FLAG_WATCHES_CHILDREN) + *flags |= FSNOTIFY_OBJ_FLAG_UPDATE_CHILDREN; + if (conn->flags & FSNOTIFY_CONN_FLAG_HAS_IREF) + *flags |= ~FSNOTIFY_OBJ_FLAG_NEED_IPUT; + if (!*flags) inode = NULL; } else if (conn->type == FSNOTIFY_OBJ_TYPE_VFSMOUNT) { fsnotify_conn_mount(conn)->mnt_fsnotify_mask = 0; @@ -280,14 +297,35 @@ static void fsnotify_final_mark_destroy(struct fsnotify_mark *mark) } /* Drop object reference originally held by a connector */ -static void fsnotify_drop_object(unsigned int type, void *objp) +static void fsnotify_drop_object(struct fsnotify_mark_connector *conn, + unsigned int type, void *objp, int flags) { if (!objp) return; /* Currently only inode references are passed to be dropped */ if (WARN_ON_ONCE(type != FSNOTIFY_OBJ_TYPE_INODE)) return; - fsnotify_put_inode_ref(objp); + + if (flags & FSNOTIFY_OBJ_FLAG_UPDATE_CHILDREN) + /* + * At this point, we've already detached the connector from the + * inode. It's entirely possible that another connector has been + * attached, and that connector would assume that the children's + * flags are all clear. There are two possibilities: + * (a) The connector has not yet attached a mark that watches its + * children. In this case, we will properly clear out the flags, + * and the connector's flags will be consistent with the + * children. + * (b) The connector attaches a mark that watches its children. + * It may have even already altered i_fsnotify_mask and/or + * altered the child dentry flags. In this case, our call here + * will read the correct value of i_fsnotify_mask and apply it + * to the children, which duplicates some work, but isn't + * harmful. + */ + fsnotify_update_children_dentry_flags(conn, objp); + if (flags & FSNOTIFY_OBJ_FLAG_NEED_IPUT) + fsnotify_put_inode_ref(objp); } void fsnotify_put_mark(struct fsnotify_mark *mark) @@ -296,6 +334,7 @@ void fsnotify_put_mark(struct fsnotify_mark *mark) void *objp = NULL; unsigned int type = FSNOTIFY_OBJ_TYPE_DETACHED; bool free_conn = false; + int flags = 0; /* Catch marks that were actually never attached to object */ if (!conn) { @@ -313,16 +352,16 @@ void fsnotify_put_mark(struct fsnotify_mark *mark) hlist_del_init_rcu(&mark->obj_list); if (hlist_empty(&conn->list)) { - objp = fsnotify_detach_connector_from_object(conn, &type); + objp = fsnotify_detach_connector_from_object(conn, &type, &flags); free_conn = true; } else { - objp = __fsnotify_recalc_mask(conn); + objp = __fsnotify_recalc_mask(conn, &flags); type = conn->type; } WRITE_ONCE(mark->connector, NULL); spin_unlock(&conn->lock); - fsnotify_drop_object(type, objp); + fsnotify_drop_object(conn, type, objp, flags); if (free_conn) { spin_lock(&destroy_lock); @@ -331,12 +370,6 @@ void fsnotify_put_mark(struct fsnotify_mark *mark) spin_unlock(&destroy_lock); queue_work(system_unbound_wq, &connector_reaper_work); } - /* - * Note that we didn't update flags telling whether inode cares about - * what's happening with children. We update these flags from - * __fsnotify_parent() lazily when next event happens on one of our - * children. - */ spin_lock(&destroy_lock); list_add(&mark->g_list, &destroy_list); spin_unlock(&destroy_lock); @@ -834,6 +867,7 @@ void fsnotify_destroy_marks(fsnotify_connp_t *connp) struct fsnotify_mark *mark, *old_mark = NULL; void *objp; unsigned int type; + int flags = 0; conn = fsnotify_grab_connector(connp); if (!conn) @@ -859,11 +893,11 @@ void fsnotify_destroy_marks(fsnotify_connp_t *connp) * mark references get dropped. It would lead to strange results such * as delaying inode deletion or blocking unmount. */ - objp = fsnotify_detach_connector_from_object(conn, &type); + objp = fsnotify_detach_connector_from_object(conn, &type, &flags); spin_unlock(&conn->lock); if (old_mark) fsnotify_put_mark(old_mark); - fsnotify_drop_object(type, objp); + fsnotify_drop_object(conn, type, objp, flags); } /* diff --git a/include/linux/fsnotify_backend.h b/include/linux/fsnotify_backend.h index d7d96c806bff..942fbcc34286 100644 --- a/include/linux/fsnotify_backend.h +++ b/include/linux/fsnotify_backend.h @@ -474,6 +474,7 @@ struct fsnotify_mark_connector { unsigned short type; /* Type of object [lock] */ #define FSNOTIFY_CONN_FLAG_HAS_FSID 0x01 #define FSNOTIFY_CONN_FLAG_HAS_IREF 0x02 +#define FSNOTIFY_CONN_FLAG_WATCHES_CHILDREN 0x04 unsigned short flags; /* flags [lock] */ __kernel_fsid_t fsid; /* fsid of filesystem containing object */ union { @@ -485,6 +486,13 @@ struct fsnotify_mark_connector { struct hlist_head list; }; +/* + * Objects may need some additional actions to be taken when the last reference + * is dropped. Define flags to indicate which actions are necessary. + */ +#define FSNOTIFY_OBJ_FLAG_NEED_IPUT 0x01 +#define FSNOTIFY_OBJ_FLAG_UPDATE_CHILDREN 0x02 + /* * A mark is simply an object attached to an in core inode which allows an * fsnotify listener to indicate they are either no longer interested in events From patchwork Fri Oct 21 01:03:10 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Stephen Brennan X-Patchwork-Id: 6466 Return-Path: Delivered-To: ouuuleilei@gmail.com Received: by 2002:a5d:4242:0:0:0:0:0 with SMTP id s2csp413715wrr; Thu, 20 Oct 2022 18:17:22 -0700 (PDT) X-Google-Smtp-Source: AMsMyM51mhniCyypuJo9MgrV1HrpBeKT5Mv0Yubf0GP//vxvM8Ba8ip5GQdpxmv/1UtOrymgRaQn X-Received: by 2002:a17:907:75f1:b0:78a:f935:647d with SMTP id jz17-20020a17090775f100b0078af935647dmr13263026ejc.587.1666315042062; Thu, 20 Oct 2022 18:17:22 -0700 (PDT) ARC-Seal: i=2; a=rsa-sha256; t=1666315042; cv=pass; d=google.com; s=arc-20160816; b=HzNzucXlwcTX6f8mh7Y3W3SGbocES0uzPpaZEvTuErzTwUO4b2G+M8wyymGkm9xCUw wqBLLdBaE7lUIFbolHW5Ziq+Y7qM23w/MtRCVSCc5+TCCiBvvHvVAQCvexdnP7Hhyom3 op9JLGZP5XP8+xwszQAvyxMCRW3O+0CtMTZ22qBp1Up6cILqx8+4TMCWd/aoc6i/rYnV mqllDGWZOrMIkMzbA/G/FyurZ3mzGN1535mswYMc1pdlmFLmDy20FGIviV9lpEQti/Hx fq1L4F2BQhX4hGabctUAuJbekalVnLOmbx7S1kuaafZCw1TQqpqQ/7N+P3pdHZ63Z6b/ tBbA== ARC-Message-Signature: i=2; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=list-id:precedence:mime-version:content-transfer-encoding :references:in-reply-to:message-id:date:subject:cc:to:from :dkim-signature:dkim-signature; bh=U4SsRmB3G9PJJFDy2/xoex3JNU0etDYF8lljuvSJL4A=; b=U74CwiKV/B5/x+1EkGjiaaBrE9A4xIFzb8L02w0qmnR02OBrdKJtBL3l21l4eqfFJ3 V+ZQofRtiwUbw+C3A/ypTSms8Ff33BjWCYQ1y0n0IlkD1wuum0I/njtrjhZVAjjAq3nD UlC7VGmV1kJyaf5xGfKnZHr2EZVOD5fVovBZvjtgDkvxnZ21dqAGd1WfnvgbVBNgJ0Ny QG615yUEGPza02RZal89oaSMMgb54aRo5Qt5m2juF8oSA2R8eSu83R1W1KOifzKt4zrO NF26qiiM4D85oNz6S6obdB2SAv6fiJQa5YauR4NjLT2gNrPPVfmREMDWgJm4eJQD/fw5 wFQA== ARC-Authentication-Results: i=2; mx.google.com; dkim=pass header.i=@oracle.com header.s=corp-2022-7-12 header.b=fo8ctwo1; dkim=pass header.i=@oracle.onmicrosoft.com header.s=selector2-oracle-onmicrosoft-com header.b=hDEjfLMo; arc=pass (i=1 spf=pass spfdomain=oracle.com dkim=pass dkdomain=oracle.com dmarc=pass fromdomain=oracle.com); spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=oracle.com Received: from out1.vger.email (out1.vger.email. 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Since iteration needs to hold parent->d_lock, this can trigger soft lockups. It would be best to make this iteration sleepable. Since we have the inode locked exclusive, we can drop the parent->d_lock and sleep, holding a reference to a child dentry, and continue iteration once we wake. Signed-off-by: Stephen Brennan --- fs/notify/fsnotify.c | 39 +++++++++++++++++++++++++++++++++++---- 1 file changed, 35 insertions(+), 4 deletions(-) diff --git a/fs/notify/fsnotify.c b/fs/notify/fsnotify.c index f83eca4fb841..061e626127ca 100644 --- a/fs/notify/fsnotify.c +++ b/fs/notify/fsnotify.c @@ -102,10 +102,12 @@ void fsnotify_sb_delete(struct super_block *sb) * on a child we run all of our children and set a dentry flag saying that the * parent cares. Thus when an event happens on a child it can quickly tell * if there is a need to find a parent and send the event to the parent. + * + * Context: inode locked exclusive */ bool __fsnotify_update_children_dentry_flags(struct inode *inode) { - struct dentry *alias, *child; + struct dentry *child, *alias, *last_ref = NULL; int watched; if (!S_ISDIR(inode->i_mode)) @@ -119,11 +121,38 @@ bool __fsnotify_update_children_dentry_flags(struct inode *inode) /* Since this is a directory, there damn well better only be one child */ alias = d_find_any_alias(inode); - /* run all of the children of the original inode and fix their - * d_flags to indicate parental interest (their parent is the - * original inode) */ + /* + * These lists can get very long, so we may need to sleep during + * iteration. Normally this would be impossible without a cursor, + * but since we have the inode locked exclusive, we're guaranteed + * that the directory won't be modified, so whichever dentry we + * pick to sleep on won't get moved. So, start a manual iteration + * over d_subdirs which will allow us to sleep. + */ spin_lock(&alias->d_lock); +retry: list_for_each_entry(child, &alias->d_subdirs, d_child) { + if (need_resched()) { + /* + * We need to hold a reference while we sleep. But when + * we wake, dput() could free the dentry, invalidating + * the list pointers. We can't look at the list pointers + * until we re-lock the parent, and we can't dput() once + * we have the parent locked. So the solution is to hold + * onto our reference and free it the *next* time we drop + * alias->d_lock: either at the end of the function, or + * at the time of the next sleep. + */ + dget(child); + spin_unlock(&alias->d_lock); + dput(last_ref); + last_ref = child; + cond_resched(); + spin_lock(&alias->d_lock); + if (child->d_parent != alias) + goto retry; + } + if (!child->d_inode) continue; @@ -135,6 +164,8 @@ bool __fsnotify_update_children_dentry_flags(struct inode *inode) spin_unlock(&child->d_lock); } spin_unlock(&alias->d_lock); + if (last_ref) + dput(last_ref); return watched; }