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jffs2: GC deadlock reading a page that is used in jffs2_write_begin() 

GC task can deadlock in read_cache_page() because it may attempt
to release a page that is actually allocated by another task in
jffs2_write_begin().
The reason is that in jffs2_write_begin() there is a small window
a cache page is allocated for use but not set Uptodate yet.

This ends up with a deadlock between two tasks:
1) A task (e.g. file copy)
   - jffs2_write_begin() locks a cache page
   - jffs2_write_end() tries to lock "alloc_sem" from
	 jffs2_reserve_space() <-- STUCK
2) GC task (jffs2_gcd_mtd3)
   - jffs2_garbage_collect_pass() locks "alloc_sem"
   - try to lock the same cache page in read_cache_page() <-- STUCK

So to avoid this deadlock, hold "alloc_sem" in jffs2_write_begin()
while reading data in a cache page.

Signed-off-by: Kyeong Yoo <kyeong.yoo@alliedtelesis.co.nz>
Signed-off-by: Richard Weinberger <richard@nod.at>
This commit is contained in:
Kyeong Yoo 2017-07-04 16:22:38 +12:00 committed by Richard Weinberger
parent 50cb437325
commit aa39cc6757
1 changed files with 25 additions and 15 deletions
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40
fs/jffs2/file.c
View File

@ -136,20 +136,15 @@ static int jffs2_write_begin(struct file *filp, struct address_space *mapping,
struct page *pg;
struct inode *inode = mapping->host;
struct jffs2_inode_info *f = JFFS2_INODE_INFO(inode);
struct jffs2_sb_info *c = JFFS2_SB_INFO(inode->i_sb);
pgoff_t index = pos >> PAGE_SHIFT;
uint32_t pageofs = index << PAGE_SHIFT;
int ret = 0;
pg = grab_cache_page_write_begin(mapping, index, flags);
if (!pg)
return -ENOMEM;
*pagep = pg;
jffs2_dbg(1, "%s()\n", __func__);
if (pageofs > inode->i_size) {
/* Make new hole frag from old EOF to new page */
struct jffs2_sb_info *c = JFFS2_SB_INFO(inode->i_sb);
struct jffs2_raw_inode ri;
struct jffs2_full_dnode *fn;
uint32_t alloc_len;
@ -160,7 +155,7 @@ static int jffs2_write_begin(struct file *filp, struct address_space *mapping,
ret = jffs2_reserve_space(c, sizeof(ri), &alloc_len,
ALLOC_NORMAL, JFFS2_SUMMARY_INODE_SIZE);
if (ret)
goto out_page;
goto out_err;
mutex_lock(&f->sem);
memset(&ri, 0, sizeof(ri));
@ -190,7 +185,7 @@ static int jffs2_write_begin(struct file *filp, struct address_space *mapping,
ret = PTR_ERR(fn);
jffs2_complete_reservation(c);
mutex_unlock(&f->sem);
goto out_page;
goto out_err;
}
ret = jffs2_add_full_dnode_to_inode(c, f, fn);
if (f->metadata) {
@ -205,13 +200,26 @@ static int jffs2_write_begin(struct file *filp, struct address_space *mapping,
jffs2_free_full_dnode(fn);
jffs2_complete_reservation(c);
mutex_unlock(&f->sem);
goto out_page;
goto out_err;
}
jffs2_complete_reservation(c);
inode->i_size = pageofs;
mutex_unlock(&f->sem);
}
/*
* While getting a page and reading data in, lock c->alloc_sem until
* the page is Uptodate. Otherwise GC task may attempt to read the same
* page in read_cache_page(), which causes a deadlock.
*/
mutex_lock(&c->alloc_sem);
pg = grab_cache_page_write_begin(mapping, index, flags);
if (!pg) {
ret = -ENOMEM;
goto release_sem;
}
*pagep = pg;
/*
* Read in the page if it wasn't already present. Cannot optimize away
* the whole page write case until jffs2_write_end can handle the
@ -221,15 +229,17 @@ static int jffs2_write_begin(struct file *filp, struct address_space *mapping,
mutex_lock(&f->sem);
ret = jffs2_do_readpage_nolock(inode, pg);
mutex_unlock(&f->sem);
if (ret)
goto out_page;
if (ret) {
unlock_page(pg);
put_page(pg);
goto release_sem;
}
}
jffs2_dbg(1, "end write_begin(). pg->flags %lx\n", pg->flags);
return ret;
out_page:
unlock_page(pg);
put_page(pg);
release_sem:
mutex_unlock(&c->alloc_sem);
out_err:
return ret;
}