kernel.git/fs/dcache.c, branch linux-4.12.y

dentry name snapshots

2017-08-06T16:21:11Z

commit 49d31c2f389acfe83417083e1208422b4091cd9e upstream. take_dentry_name_snapshot() takes a safe snapshot of dentry name; if the name is a short one, it gets copied into caller-supplied structure, otherwise an extra reference to external name is grabbed (those are never modified). In either case the pointer to stable string is stored into the same structure. dentry must be held by the caller of take_dentry_name_snapshot(), but may be freely dropped afterwards - the snapshot will stay until destroyed by release_dentry_name_snapshot(). Intended use: struct name_snapshot s; take_dentry_name_snapshot(&s, dentry); ... access s.name ... release_dentry_name_snapshot(&s); Replaces fsnotify_oldname_...(), gets used in fsnotify to obtain the name to pass down with event. Signed-off-by: Al Viro Signed-off-by: Greg Kroah-Hartman

fs/dcache.c: fix spin lockup issue on nlru->lock

2017-07-21T04:59:09Z

commit b17c070fb624cf10162cf92ea5e1ec25cd8ac176 upstream. __list_lru_walk_one() acquires nlru spin lock (nlru->lock) for longer duration if there are more number of items in the lru list. As per the current code, it can hold the spin lock for upto maximum UINT_MAX entries at a time. So if there are more number of items in the lru list, then "BUG: spinlock lockup suspected" is observed in the below path: spin_bug+0x90 do_raw_spin_lock+0xfc _raw_spin_lock+0x28 list_lru_add+0x28 dput+0x1c8 path_put+0x20 terminate_walk+0x3c path_lookupat+0x100 filename_lookup+0x6c user_path_at_empty+0x54 SyS_faccessat+0xd0 el0_svc_naked+0x24 This nlru->lock is acquired by another CPU in this path - d_lru_shrink_move+0x34 dentry_lru_isolate_shrink+0x48 __list_lru_walk_one.isra.10+0x94 list_lru_walk_node+0x40 shrink_dcache_sb+0x60 do_remount_sb+0xbc do_emergency_remount+0xb0 process_one_work+0x228 worker_thread+0x2e0 kthread+0xf4 ret_from_fork+0x10 Fix this lockup by reducing the number of entries to be shrinked from the lru list to 1024 at once. Also, add cond_resched() before processing the lru list again. Link: http://marc.info/?t=149722864900001&r=1&w=2 Link: http://lkml.kernel.org/r/1498707575-2472-1-git-send-email-stummala@codeaurora.org Signed-off-by: Sahitya Tummala Suggested-by: Jan Kara Suggested-by: Vladimir Davydov Acked-by: Vladimir Davydov Cc: Alexander Polakov Cc: Al Viro Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman

Hang/soft lockup in d_invalidate with simultaneous calls

2017-06-15T10:52:09Z

It's not hard to trigger a bunch of d_invalidate() on the same dentry in parallel. They end up fighting each other - any dentry picked for removal by one will be skipped by the rest and we'll go for the next iteration through the entire subtree, even if everything is being skipped. Morevoer, we immediately go back to scanning the subtree. The only thing we really need is to dissolve all mounts in the subtree and as soon as we've nothing left to do, we can just unhash the dentry and bugger off. Signed-off-by: Al Viro

fs: don't set *REFERENCED on single use objects

2017-05-03T15:47:05Z

By default we set DCACHE_REFERENCED and I_REFERENCED on any dentry or inode we create. This is problematic as this means that it takes two trips through the LRU for any of these objects to be reclaimed, regardless of their actual lifetime. With enough pressure from these caches we can easily evict our working set from page cache with single use objects. So instead only set *REFERENCED if we've already been added to the LRU list. This means that we've been touched since the first time we were accessed, and so more likely to need to hang out in cache. To illustrate this issue I wrote the following scripts https://github.com/josefbacik/debug-scripts/tree/master/cache-pressure on my test box. It is a single socket 4 core CPU with 16gib of RAM and I tested on an Intel 2tib NVME drive. The cache-pressure.sh script creates a new file system and creates 2 6.5gib files in order to take up 13gib of the 16gib of ram with pagecache. Then it runs a test program that reads these 2 files in a loop, and keeps track of how often it has to read bytes for each loop. On an ideal system with no pressure we should have to read 0 bytes indefinitely. The second thing this script does is start a fs_mark job that creates a ton of 0 length files, putting pressure on the system with slab only allocations. On exit the script prints out how many bytes were read by the read-file program. The results are as follows Without patch: /mnt/btrfs-test/reads/file1: total read during loops 27262988288 /mnt/btrfs-test/reads/file2: total read during loops 27262976000 With patch: /mnt/btrfs-test/reads/file2: total read during loops 18640457728 /mnt/btrfs-test/reads/file1: total read during loops 9565376512 This patch results in a 50% reduction of the amount of pages evicted from our working set. Signed-off-by: Josef Bacik Signed-off-by: Al Viro

mnt: Protect the mountpoint hashtable with mount_lock

2017-01-10T00:34:43Z

Protecting the mountpoint hashtable with namespace_sem was sufficient until a call to umount_mnt was added to mntput_no_expire. At which point it became possible for multiple calls of put_mountpoint on the same hash chain to happen on the same time. Kristen Johansen reported: > This can cause a panic when simultaneous callers of put_mountpoint > attempt to free the same mountpoint. This occurs because some callers > hold the mount_hash_lock, while others hold the namespace lock. Some > even hold both. > > In this submitter's case, the panic manifested itself as a GP fault in > put_mountpoint() when it called hlist_del() and attempted to dereference > a m_hash.pprev that had been poisioned by another thread. Al Viro observed that the simple fix is to switch from using the namespace_sem to the mount_lock to protect the mountpoint hash table. I have taken Al's suggested patch moved put_mountpoint in pivot_root (instead of taking mount_lock an additional time), and have replaced new_mountpoint with get_mountpoint a function that does the hash table lookup and addition under the mount_lock. The introduction of get_mounptoint ensures that only the mount_lock is needed to manipulate the mountpoint hashtable. d_set_mounted is modified to only set DCACHE_MOUNTED if it is not already set. This allows get_mountpoint to use the setting of DCACHE_MOUNTED to ensure adding a struct mountpoint for a dentry happens exactly once. Cc: stable@vger.kernel.org Fixes: ce07d891a089 ("mnt: Honor MNT_LOCKED when detaching mounts") Reported-by: Krister Johansen Suggested-by: Al Viro Acked-by: Al Viro Signed-off-by: "Eric W. Biederman"

Replace with globally

2016-12-24T19:46:01Z

This was entirely automated, using the script by Al: PATT='^[[:blank:]]*#[[:blank:]]*include[[:blank:]]*' sed -i -e "s!$PATT!#include !" \ $(git grep -l "$PATT"|grep -v ^include/linux/uaccess.h) to do the replacement at the end of the merge window. Requested-by: Al Viro Signed-off-by: Linus Torvalds

vfs: remove unused have_submounts() function

2016-12-04T01:51:49Z

Now that path_has_submounts() has been added have_submounts() is no longer used so remove it. Link: http://lkml.kernel.org/r/20161011053428.27645.12310.stgit@pluto.themaw.net Signed-off-by: Ian Kent Cc: Al Viro Cc: Eric W. Biederman Cc: Omar Sandoval Signed-off-by: Andrew Morton Signed-off-by: Al Viro

vfs: add path_has_submounts()

2016-12-04T01:51:47Z

d_mountpoint() can only be used reliably to establish if a dentry is not mounted in any namespace. It isn't aware of the possibility there may be multiple mounts using the given dentry, possibly in a different namespace. Add function, path_has_submounts(), that checks is a struct path contains mounts (or is a mountpoint itself) to handle this case. Link: http://lkml.kernel.org/r/20161011053403.27645.55242.stgit@pluto.themaw.net Signed-off-by: Ian Kent Cc: Al Viro Cc: Eric W. Biederman Cc: Omar Sandoval Signed-off-by: Andrew Morton Signed-off-by: Al Viro

Merge branch 'for-linus-2' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs

2016-08-07T14:01:14Z

Pull more vfs updates from Al Viro: "Assorted cleanups and fixes. In the "trivial API change" department - ->d_compare() losing 'parent' argument" * 'for-linus-2' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs: cachefiles: Fix race between inactivating and culling a cache object 9p: use clone_fid() 9p: fix braino introduced in "9p: new helper - v9fs_parent_fid()" vfs: make dentry_needs_remove_privs() internal vfs: remove file_needs_remove_privs() vfs: fix deadlock in file_remove_privs() on overlayfs get rid of 'parent' argument of ->d_compare() cifs, msdos, vfat, hfs+: don't bother with parent in ->d_compare() affs ->d_compare(): don't bother with ->d_inode fold _d_rehash() and __d_rehash() together fold dentry_rcuwalk_invalidate() into its only remaining caller

Merge branch 'work.const-qstr' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs

2016-08-06T13:49:02Z

Pull qstr constification updates from Al Viro: "Fairly self-contained bunch - surprising lot of places passes struct qstr * as an argument when const struct qstr * would suffice; it complicates analysis for no good reason. I'd prefer to feed that separately from the assorted fixes (those are in #for-linus and with somewhat trickier topology)" * 'work.const-qstr' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs: qstr: constify instances in adfs qstr: constify instances in lustre qstr: constify instances in f2fs qstr: constify instances in ext2 qstr: constify instances in vfat qstr: constify instances in procfs qstr: constify instances in fuse qstr constify instances in fs/dcache.c qstr: constify instances in nfs qstr: constify instances in ocfs2 qstr: constify instances in autofs4 qstr: constify instances in hfs qstr: constify instances in hfsplus qstr: constify instances in logfs qstr: constify dentry_init_security