Merge tag 'erofs-for-7.2-rc6-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/xiang/erofs

Pull erofs fixes from Gao Xiang:
 "Fix a regression in page cache sharing which can cause a NULL pointer
  dereference, and limit LZMA stream memory usage on systems with many
  CPUs.

   - Keep a valid f_path for page cache sharing to fix a recent
     mincore() NULL pointer dereference

   - Limit LZMA stream pool size when too many processors are available

   - Sync up with Hongbo Li's latest email address"

* tag 'erofs-for-7.2-rc6-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/xiang/erofs:
  erofs: cap LZMA stream pool size
  erofs: ensure valid f_path for page cache sharing
  MAINTAINERS: update Hongbo Li's email address

5 files changed, 48 insertions, 34 deletions

diff --git a/MAINTAINERS b/MAINTAINERS
index 716acfc3d7c1..2f9472c1a090 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -9617,7 +9617,7 @@ M:	Chao Yu <chao@kernel.org>
 R:	Yue Hu <zbestahu@gmail.com>
 R:	Jeffle Xu <jefflexu@linux.alibaba.com>
 R:	Sandeep Dhavale <dhavale@google.com>
-R:	Hongbo Li <lihongbo22@huawei.com>
+R:	Hongbo Li <hongbohbli@tencent.com>
 R:	Chunhai Guo <guochunhai@vivo.com>
 L:	linux-erofs@lists.ozlabs.org
 S:	Maintained
diff --git a/fs/erofs/Kconfig b/fs/erofs/Kconfig
index 4789b1077d8c..8ca1767dafb6 100644
--- a/fs/erofs/Kconfig
+++ b/fs/erofs/Kconfig
@@ -131,6 +131,20 @@ config EROFS_FS_ZIP_LZMA
 
 	  Say N if you want to disable LZMA compression support.
 
+config EROFS_FS_ZIP_LZMA_DEFAULT_MAX_STREAMS
+	int "EROFS LZMA default maximum decompression streams"
+	depends on EROFS_FS_ZIP_LZMA
+	range 1 NR_CPUS
+	default 16
+	help
+	  By default EROFS allocates one LZMA decompression stream per CPU.
+	  Each stream can hold a dictionary of up to 8 MiB taken from the
+	  mounted image, so on systems with many CPUs this can reserve a lot
+	  of memory.  This caps the default; the lzma_streams module parameter
+	  still overrides it.
+
+	  If unsure, keep the default of 16.
+
 config EROFS_FS_ZIP_DEFLATE
 	bool "EROFS DEFLATE compressed data support"
 	depends on EROFS_FS_ZIP
@@ -189,6 +203,7 @@ config EROFS_FS_PCPU_KTHREAD_HIPRI
 config EROFS_FS_PAGE_CACHE_SHARE
 	bool "EROFS page cache share support (experimental)"
 	depends on EROFS_FS && EROFS_FS_XATTR
+	select FS_STACK
 	help
 	  This enables page cache sharing among inodes with identical
 	  content fingerprints on the same machine.
diff --git a/fs/erofs/decompressor_lzma.c b/fs/erofs/decompressor_lzma.c
index f6692d0f2f04..6b0cdb446c6a 100644
--- a/fs/erofs/decompressor_lzma.c
+++ b/fs/erofs/decompressor_lzma.c
@@ -51,7 +51,8 @@ static int __init z_erofs_lzma_init(void)
 
 	/* by default, use # of possible CPUs instead */
 	if (!z_erofs_lzma_nstrms)
-		z_erofs_lzma_nstrms = num_possible_cpus();
+		z_erofs_lzma_nstrms = min_t(unsigned int, num_possible_cpus(),
+				CONFIG_EROFS_FS_ZIP_LZMA_DEFAULT_MAX_STREAMS);
 
 	for (i = 0; i < z_erofs_lzma_nstrms; ++i) {
 		struct z_erofs_lzma *strm = kzalloc_obj(*strm);
diff --git a/fs/erofs/internal.h b/fs/erofs/internal.h
index 580f8d9f14e7..57bd21859c65 100644
--- a/fs/erofs/internal.h
+++ b/fs/erofs/internal.h
@@ -288,8 +288,8 @@ struct erofs_inode {
 			struct erofs_inode_fingerprint fingerprint;
 			spinlock_t ishare_lock;
 		};
-		/* for each real inode */
-		struct inode *sharedinode;
+		/* for each real filesystem inode */
+		struct dentry *sharedentry;
 	};
 #endif
 	/* the corresponding vfs inode */
diff --git a/fs/erofs/ishare.c b/fs/erofs/ishare.c
index a1a20a5ba548..fa7d4112dec5 100644
--- a/fs/erofs/ishare.c
+++ b/fs/erofs/ishare.c
@@ -2,14 +2,13 @@
 /*
  * Copyright (C) 2024, Alibaba Cloud
  */
+#include <linux/backing-file.h>
 #include <linux/xxhash.h>
 #include <linux/mount.h>
 #include <linux/security.h>
 #include "internal.h"
 #include "xattr.h"
 
-#include "../internal.h"
-
 static struct vfsmount *erofs_ishare_mnt;
 
 static int erofs_ishare_iget5_eq(struct inode *inode, void *data)
@@ -33,10 +32,12 @@ static int erofs_ishare_iget5_set(struct inode *inode, void *data)
 
 bool erofs_ishare_fill_inode(struct inode *inode)
 {
+	static const struct file_operations empty_fops = {};
 	struct erofs_sb_info *sbi = EROFS_SB(inode->i_sb);
 	const struct address_space_operations *aops;
 	struct erofs_inode *vi = EROFS_I(inode);
 	struct erofs_inode_fingerprint fp;
+	struct dentry *sd;
 	struct inode *si;
 
 	aops = erofs_get_aops(inode);
@@ -49,7 +50,9 @@ bool erofs_ishare_fill_inode(struct inode *inode)
 			  xxh32(fp.opaque, fp.size, 0),
 			  erofs_ishare_iget5_eq, erofs_ishare_iget5_set, &fp);
 	if (si && (inode_state_read_once(si) & I_NEW)) {
+		si->i_fop = &empty_fops;
 		si->i_mapping->a_ops = aops;
+		si->i_mode = 0444 | S_IFREG;
 		si->i_size = inode->i_size;
 		unlock_new_inode(si);
 	} else {
@@ -65,7 +68,10 @@ bool erofs_ishare_fill_inode(struct inode *inode)
 			return false;
 		}
 	}
-	vi->sharedinode = si;
+	sd = d_obtain_alias(si); /* disconnected denties for sharedinodes */
+	if (IS_ERR(sd))
+		return false;
+	vi->sharedentry = sd;
 	INIT_LIST_HEAD(&vi->ishare_list);
 	spin_lock(&EROFS_I(si)->ishare_lock);
 	list_add(&vi->ishare_list, &EROFS_I(si)->ishare_list);
@@ -75,48 +81,40 @@ bool erofs_ishare_fill_inode(struct inode *inode)
 
 void erofs_ishare_free_inode(struct inode *inode)
 {
-	struct erofs_inode *vi = EROFS_I(inode);
-	struct inode *sharedinode = vi->sharedinode;
+	struct erofs_inode *vi = EROFS_I(inode), *svi;
 
-	if (!sharedinode)
+	if (!vi->sharedentry)
 		return;
-	spin_lock(&EROFS_I(sharedinode)->ishare_lock);
+	svi = EROFS_I(d_inode(vi->sharedentry));
+	spin_lock(&svi->ishare_lock);
 	list_del(&vi->ishare_list);
-	spin_unlock(&EROFS_I(sharedinode)->ishare_lock);
-	iput(sharedinode);
-	vi->sharedinode = NULL;
+	spin_unlock(&svi->ishare_lock);
+	dput(vi->sharedentry);
+	vi->sharedentry = NULL;
 }
 
 static int erofs_ishare_file_open(struct inode *inode, struct file *file)
 {
-	struct inode *sharedinode = EROFS_I(inode)->sharedinode;
-	struct file *realfile;
+	struct path sharedpath = {
+		.mnt = erofs_ishare_mnt,
+		.dentry = EROFS_I(inode)->sharedentry,
+	};
+	struct file *rf;
 
 	if (file->f_flags & O_DIRECT)
 		return -EINVAL;
-	realfile = alloc_empty_backing_file(O_RDONLY|O_NOATIME, current_cred(),
-					    file);
-	if (IS_ERR(realfile))
-		return PTR_ERR(realfile);
-	ihold(sharedinode);
-	realfile->f_op = &erofs_file_fops;
-	realfile->f_inode = sharedinode;
-	realfile->f_mapping = sharedinode->i_mapping;
-	path_get(&file->f_path);
-	backing_file_set_user_path(realfile, &file->f_path);
-
-	file_ra_state_init(&realfile->f_ra, file->f_mapping);
-	realfile->private_data = EROFS_I(inode);
-	file->private_data = realfile;
+
+	rf = backing_file_open(file, file->f_flags | O_NOATIME,
+			       &sharedpath, current_cred());
+	if (IS_ERR(rf))
+		return PTR_ERR(rf);
+	file->private_data = rf;
 	return 0;
 }
 
 static int erofs_ishare_file_release(struct inode *inode, struct file *file)
 {
-	struct file *realfile = file->private_data;
-
-	iput(realfile->f_inode);
-	fput(realfile);
+	fput(file->private_data);
 	file->private_data = NULL;
 	return 0;
 }