From: Al Viro Date: Wed, 8 Jul 2015 01:42:38 +0000 (+0100) Subject: freeing unlinked file indefinitely delayed X-Git-Url: https://git.stricted.de/?a=commitdiff_plain;h=75a6f82a0d10ef8f13cd8fe7212911a0252ab99e;p=GitHub%2Fmoto-9609%2Fandroid_kernel_motorola_exynos9610.git freeing unlinked file indefinitely delayed Normally opening a file, unlinking it and then closing will have the inode freed upon close() (provided that it's not otherwise busy and has no remaining links, of course). However, there's one case where that does *not* happen. Namely, if you open it by fhandle with cold dcache, then unlink() and close(). In normal case you get d_delete() in unlink(2) notice that dentry is busy and unhash it; on the final dput() it will be forcibly evicted from dcache, triggering iput() and inode removal. In this case, though, we end up with *two* dentries - disconnected (created by open-by-fhandle) and regular one (used by unlink()). The latter will have its reference to inode dropped just fine, but the former will not - it's considered hashed (it is on the ->s_anon list), so it will stay around until the memory pressure will finally do it in. As the result, we have the final iput() delayed indefinitely. It's trivial to reproduce - void flush_dcache(void) { system("mount -o remount,rw /"); } static char buf[20 * 1024 * 1024]; main() { int fd; union { struct file_handle f; char buf[MAX_HANDLE_SZ]; } x; int m; x.f.handle_bytes = sizeof(x); chdir("/root"); mkdir("foo", 0700); fd = open("foo/bar", O_CREAT | O_RDWR, 0600); close(fd); name_to_handle_at(AT_FDCWD, "foo/bar", &x.f, &m, 0); flush_dcache(); fd = open_by_handle_at(AT_FDCWD, &x.f, O_RDWR); unlink("foo/bar"); write(fd, buf, sizeof(buf)); system("df ."); /* 20Mb eaten */ close(fd); system("df ."); /* should've freed those 20Mb */ flush_dcache(); system("df ."); /* should be the same as #2 */ } will spit out something like Filesystem 1K-blocks Used Available Use% Mounted on /dev/root 322023 303843 1131 100% / Filesystem 1K-blocks Used Available Use% Mounted on /dev/root 322023 303843 1131 100% / Filesystem 1K-blocks Used Available Use% Mounted on /dev/root 322023 283282 21692 93% / - inode gets freed only when dentry is finally evicted (here we trigger than by remount; normally it would've happened in response to memory pressure hell knows when). Cc: stable@vger.kernel.org # v2.6.38+; earlier ones need s/kill_it/unhash_it/ Acked-by: J. Bruce Fields Signed-off-by: Al Viro --- diff --git a/fs/dcache.c b/fs/dcache.c index 7a3f3e5f9cea..5c8ea15e73a5 100644 --- a/fs/dcache.c +++ b/fs/dcache.c @@ -642,7 +642,7 @@ static inline bool fast_dput(struct dentry *dentry) /* * If we have a d_op->d_delete() operation, we sould not - * let the dentry count go to zero, so use "put__or_lock". + * let the dentry count go to zero, so use "put_or_lock". */ if (unlikely(dentry->d_flags & DCACHE_OP_DELETE)) return lockref_put_or_lock(&dentry->d_lockref); @@ -697,7 +697,7 @@ static inline bool fast_dput(struct dentry *dentry) */ smp_rmb(); d_flags = ACCESS_ONCE(dentry->d_flags); - d_flags &= DCACHE_REFERENCED | DCACHE_LRU_LIST; + d_flags &= DCACHE_REFERENCED | DCACHE_LRU_LIST | DCACHE_DISCONNECTED; /* Nothing to do? Dropping the reference was all we needed? */ if (d_flags == (DCACHE_REFERENCED | DCACHE_LRU_LIST) && !d_unhashed(dentry)) @@ -776,6 +776,9 @@ repeat: if (unlikely(d_unhashed(dentry))) goto kill_it; + if (unlikely(dentry->d_flags & DCACHE_DISCONNECTED)) + goto kill_it; + if (unlikely(dentry->d_flags & DCACHE_OP_DELETE)) { if (dentry->d_op->d_delete(dentry)) goto kill_it;