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squashfs_cache_get() puts a task to sleep when its block is not cached and
every cache entry is busy. Those sleeps are non-exclusive, so the
nr_exclusive == 1 budget squashfs_cache_put() has always passed to
wake_up() is inert and one release makes every waiter runnable. A wakee
only returns to squashfs_cache_get() if it observes cache->unused before
the entry is reclaimed; later wakees see zero and re-queue inside
wait_event() without rescanning. One freed entry satisfies exactly one
capacity waiter, so waking the rest is waste.
On a Meta production host serving a Python web application from a packaged
squashfs image, a 30-second trace caught 1,045,132 cache-release wake
calls and 19,511,556 wakeups: 18.7 per release, although each release
added only one reusable cache entry. This was causing significant spikes
in CPU usage.
Make the waits exclusive, enqueueing while still holding cache->lock so
that a concurrent lookup either sees the waiter queued or the waiter sees
the block that lookup publishes. Two things follow.
A wakee cannot be assumed to consume the entry it was woken for: it may
find its own block published meanwhile, share that entry, and leave the
freed one unclaimed. So a wakee which shares hands its wakeup on to the
next waiter, as commit 0ddad21d3e99 ("pipe: use exclusive waits when
reading or writing") does with wake_next_reader.
And a waiter can now sleep through a publication of the very block it
wants, which the old broadcast gave it repeated chances to notice. So
waiters are keyed by block: publishing wakes every waiter for that block
(nr_exclusive == 0), freeing an entry wakes one. That needs a custom wake
callback, like wake_page_function() in mm/filemap.c, which also records
which wakeup arrived so the handoff only fires for a capacity wakee.
Broadcast is kept where more than one task can proceed - every waiter for
a published block, and the wake_up_all() on entry->wait_queue - at the
cost of walking the queue under wait_queue.lock to test the key. Waiters
are now served FIFO with a scheduling round trip per handoff hop, so
per-waiter latency changes; the filebench run below is 4x oversubscribed,
where that should hurt most.
Measured on a 32-CPU VM against a read-only squashfs (gzip,
DECOMP_MULTI_PERCPU, FILE_DIRECT, default 8 metadata / 3 fragment cache
entries) staged in tmpfs, page cache dropped each iteration to force cold
decompression:
elbencho, 64 threads
metadata stat 700 -> 1320 files/s 1.9x
small-file read 40 -> 60 MiB/s 1.5x
filebench, 128 threads, open+read+stat+close (mean of 3x 30s)
throughput 11,314 -> 25,186 ops/s 2.2x
sched:sched_wakeup 27.0 -> 4.55 per op 5.9x fewer
context switches 37.2 -> 7.64 per op 4.9x fewer
Wakeups and context switches are per operation, since the two runs did
2.2x different amounts of work. Workloads which never queue for a cache
entry gain no wakeups.
Link: https://lore.kernel.org/20260807172421.3875982-1-usama.arif@linux.dev
Signed-off-by: Usama Arif <usama.arif@linux.dev>
Reviewed-by: Phillip Lougher <phillip@squashfs.org.uk>
Cc: Boris Burkov <boris@bur.io>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Jeff Layton <jlayton@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Rik van Riel <riel@surriel.com>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
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If a negative offset is read off disk (for example the offset into the
decompressed fragment block), this will cause squashfs_copy_data() to
perform an out of bounds access.
Fix by checking if offset is negative, and returning 0. This matches
existing behaviour where an offset beyond the block returns 0 bytes
copied.
To trigger this out of bounds access requires a crafted Squashfs
filesystem and CAP_SYS_ADMIN to mount it. Unprivileged users will not be
able to mount such a filesystem, but once mounted, an unprivileged user
can trigger the out of bounds access by reading the crafted file with the
negative offset.
Link: https://lore.kernel.org/20260807162951.672510-1-phillip@squashfs.org.uk
Fixes: f400e12656ab ("Squashfs: cache operations")
Signed-off-by: Phillip Lougher <phillip@squashfs.org.uk>
Reported-by: Yuejie Shi <syjcnss@gmail.com>
Closes: https://lore.kernel.org/all/20260803032735.81785-1-syjcnss@gmail.com/
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
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Syzkaller reports a "general protection fault in squashfs_copy_data"
This is ultimately caused by a corrupted index look-up table, which
produces a negative metadata block offset.
This is subsequently passed to squashfs_copy_data (via
squashfs_read_metadata) where the negative offset causes an out of bounds
access.
The fix is to check that the offset is within range in
squashfs_read_metadata. This will trap this and other cases.
Link: https://lkml.kernel.org/r/20260217050955.138351-1-phillip@squashfs.org.uk
Fixes: f400e12656ab ("Squashfs: cache operations")
Reported-by: syzbot+a9747fe1c35a5b115d3f@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/all/699234e2.a70a0220.2c38d7.00e2.GAE@google.com/
Signed-off-by: Phillip Lougher <phillip@squashfs.org.uk>
Cc: Christian Brauner <brauner@kernel.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
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This was done entirely with mindless brute force, using
git grep -l '\<k[vmz]*alloc_objs*(.*, GFP_KERNEL)' |
xargs sed -i 's/\(alloc_objs*(.*\), GFP_KERNEL)/\1)/'
to convert the new alloc_obj() users that had a simple GFP_KERNEL
argument to just drop that argument.
Note that due to the extreme simplicity of the scripting, any slightly
more complex cases spread over multiple lines would not be triggered:
they definitely exist, but this covers the vast bulk of the cases, and
the resulting diff is also then easier to check automatically.
For the same reason the 'flex' versions will be done as a separate
conversion.
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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This is the result of running the Coccinelle script from
scripts/coccinelle/api/kmalloc_objs.cocci. The script is designed to
avoid scalar types (which need careful case-by-case checking), and
instead replace kmalloc-family calls that allocate struct or union
object instances:
Single allocations: kmalloc(sizeof(TYPE), ...)
are replaced with: kmalloc_obj(TYPE, ...)
Array allocations: kmalloc_array(COUNT, sizeof(TYPE), ...)
are replaced with: kmalloc_objs(TYPE, COUNT, ...)
Flex array allocations: kmalloc(struct_size(PTR, FAM, COUNT), ...)
are replaced with: kmalloc_flex(*PTR, FAM, COUNT, ...)
(where TYPE may also be *VAR)
The resulting allocations no longer return "void *", instead returning
"TYPE *".
Signed-off-by: Kees Cook <kees@kernel.org>
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When mounting a squashfs fails, squashfs_cache_init() may return an error
pointer (e.g., -ENOMEM) instead of NULL. However, squashfs_cache_delete()
only checks for a NULL cache, and attempts to dereference the invalid
pointer. This leads to a kernel crash (BUG: unable to handle kernel
paging request in squashfs_cache_delete).
This patch fixes the issue by checking IS_ERR(cache) before accessing it.
Link: https://lkml.kernel.org/r/20250306132855.2030-1-zhiyuzhang999@gmail.com
Fixes: 49ff29240ebb ("squashfs: make squashfs_cache_init() return ERR_PTR(-ENOMEM)")
Signed-off-by: Zhiyu Zhang <zhiyuzhang999@gmail.com>
Reported-by: Zhiyu Zhang <zhiyuzhang999@gmail.com>
Closes: https://lore.kernel.org/linux-fsdevel/CALf2hKvaq8B4u5yfrE+BYt7aNguao99mfWxHngA+=o5hwzjdOg@mail.gmail.com/
Tested-by: Zhiyu Zhang <zhiyuzhang999@gmail.com>
Reviewed-by: Phillip Lougher <phillip@squashfs.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
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Patch series "squashfs: reduce memory usage and update docs".
This patchset reduces the amount of memory that Squashfs uses when
CONFIG_FILE_DIRECT is configured, and updates various out of date
information in the documentation and Kconfig.
This patch (of 4):
Make squashfs_cache_init() return an ERR_PTR(-ENOMEM) on failure rather
than NULL.
This tidies up some calling code, but, it also allows NULL to be returned
as a valid result when a cache hasn't be allocated.
Link: https://lkml.kernel.org/r/20241229233752.54481-1-phillip@squashfs.org.uk
Link: https://lkml.kernel.org/r/20241229233752.54481-2-phillip@squashfs.org.uk
Signed-off-by: Phillip Lougher <phillip@squashfs.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
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Based on 1 normalized pattern(s):
this program is free software you can redistribute it and or modify
it under the terms of the gnu general public license as published by
the free software foundation either version 2 or at your option any
later version this program is distributed in the hope that it will
be useful but without any warranty without even the implied warranty
of merchantability or fitness for a particular purpose see the gnu
general public license for more details you should have received a
copy of the gnu general public license along with this program if
not write to the free software foundation 51 franklin street fifth
floor boston ma 02110 1301 usa
extracted by the scancode license scanner the SPDX license identifier
GPL-2.0-or-later
has been chosen to replace the boilerplate/reference in 23 file(s).
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Allison Randal <allison@lohutok.net>
Reviewed-by: Kate Stewart <kstewart@linuxfoundation.org>
Cc: linux-spdx@vger.kernel.org
Link: https://lkml.kernel.org/r/20190520170857.458548087@linutronix.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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Anatoly Trosinenko reports that a corrupted squashfs image can cause a
kernel oops. It turns out that squashfs can end up being confused about
negative fragment lengths.
The regular squashfs_read_data() does check for negative lengths, but
squashfs_read_metadata() did not, and the fragment size code just
blindly trusted the on-disk value. Fix both the fragment parsing and
the metadata reading code.
Reported-by: Anatoly Trosinenko <anatoly.trosinenko@gmail.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Phillip Lougher <phillip@squashfs.org.uk>
Cc: stable@kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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Mostly direct substitution with occasional adjustment or removing
outdated comments.
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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PAGE_CACHE_{SIZE,SHIFT,MASK,ALIGN} macros were introduced *long* time
ago with promise that one day it will be possible to implement page
cache with bigger chunks than PAGE_SIZE.
This promise never materialized. And unlikely will.
We have many places where PAGE_CACHE_SIZE assumed to be equal to
PAGE_SIZE. And it's constant source of confusion on whether
PAGE_CACHE_* or PAGE_* constant should be used in a particular case,
especially on the border between fs and mm.
Global switching to PAGE_CACHE_SIZE != PAGE_SIZE would cause to much
breakage to be doable.
Let's stop pretending that pages in page cache are special. They are
not.
The changes are pretty straight-forward:
- <foo> << (PAGE_CACHE_SHIFT - PAGE_SHIFT) -> <foo>;
- <foo> >> (PAGE_CACHE_SHIFT - PAGE_SHIFT) -> <foo>;
- PAGE_CACHE_{SIZE,SHIFT,MASK,ALIGN} -> PAGE_{SIZE,SHIFT,MASK,ALIGN};
- page_cache_get() -> get_page();
- page_cache_release() -> put_page();
This patch contains automated changes generated with coccinelle using
script below. For some reason, coccinelle doesn't patch header files.
I've called spatch for them manually.
The only adjustment after coccinelle is revert of changes to
PAGE_CAHCE_ALIGN definition: we are going to drop it later.
There are few places in the code where coccinelle didn't reach. I'll
fix them manually in a separate patch. Comments and documentation also
will be addressed with the separate patch.
virtual patch
@@
expression E;
@@
- E << (PAGE_CACHE_SHIFT - PAGE_SHIFT)
+ E
@@
expression E;
@@
- E >> (PAGE_CACHE_SHIFT - PAGE_SHIFT)
+ E
@@
@@
- PAGE_CACHE_SHIFT
+ PAGE_SHIFT
@@
@@
- PAGE_CACHE_SIZE
+ PAGE_SIZE
@@
@@
- PAGE_CACHE_MASK
+ PAGE_MASK
@@
expression E;
@@
- PAGE_CACHE_ALIGN(E)
+ PAGE_ALIGN(E)
@@
expression E;
@@
- page_cache_get(E)
+ get_page(E)
@@
expression E;
@@
- page_cache_release(E)
+ put_page(E)
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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Further generalise the decompressors by adding a page handler
abstraction. This adds helpers to allow the decompressors
to access and process the output buffers in an implementation
independant manner.
This allows different types of output buffer to be passed
to the decompressors, with the implementation specific
aspects handled at decompression time, but without the
knowledge being held in the decompressor wrapper code.
This will allow the decompressors to handle Squashfs
cache buffers, and page cache pages.
This patch adds the abstraction and an implementation for
the caches.
Signed-off-by: Phillip Lougher <phillip@squashfs.org.uk>
Reviewed-by: Minchan Kim <minchan@kernel.org>
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squashfs_cache_get() iterates over all entries to search for
block its looking for. Often get() / put() are called for
same block.
If we cache the current entry index, then we can optimise the
subsequent *_get() calls.
Signed-off-by: Ajeet Yadav <ajeet.yadav.77@gmail.com>
Signed-off-by: Phillip Lougher <phillip@squashfs.org.uk>
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squashfs_read_metadata forgets to release the cache block if
an error has occurred.
Signed-off-by: Phillip Lougher <phillip@squashfs.org.uk>
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* git://git.kernel.org/pub/scm/linux/kernel/git/pkl/squashfs-linus:
Squashfs: update email address
Squashfs: add extra sanity checks at mount time
Squashfs: add sanity checks to fragment reading at mount time
Squashfs: add sanity checks to lookup table reading at mount time
Squashfs: add sanity checks to id reading at mount time
Squashfs: add sanity checks to xattr reading at mount time
Squashfs: reverse order of filesystem table reading
Squashfs: move table allocation into squashfs_read_table()
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My existing email address may stop working in a month or two, so update
email to one that will continue working.
Signed-off-by: Phillip Lougher <phillip@lougher.demon.co.uk>
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This eliminates a lot of duplicate code.
Signed-off-by: Phillip Lougher <phillip@lougher.demon.co.uk>
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- kenrel -> kernel
- whetehr -> whether
- ttt -> tt
- sss -> ss
Signed-off-by: Justin P. Mattock <justinmattock@gmail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
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Fixes generated by 'codespell' and manually reviewed.
Signed-off-by: Lucas De Marchi <lucas.demarchi@profusion.mobi>
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Move squashfs_i() definition out of squashfs.h, this eliminates
the need to #include squashfs_fs_i.h from numerous files.
Signed-off-by: Phillip Lougher <phillip@lougher.demon.co.uk>
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Move zlib buffer init/destroy code into separate wrapper file. Also
make zlib z_stream field a void * removing the need to include zlib.h
for most files.
Signed-off-by: Phillip Lougher <phillip@lougher.demon.co.uk>
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Squashfs is broken on any system where the page size is larger than
the metadata size (8192). This is easily fixed by ensuring cache->pages
is always > 0.
[akpm@linux-foundation.org: coding-style fixes]
Signed-off-by: Doug Chapman <doug.chapman@hp.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Phillip Lougher <phillip@lougher.demon.co.uk>
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This fixes a code regression caused by the recent mainlining changes.
The recent code changes call zlib_inflate repeatedly, decompressing into
separate 4K buffers, this code didn't check for the possibility that
zlib_inflate might ask for too many buffers when decompressing corrupted
data.
Signed-off-by: Phillip Lougher <phillip@lougher.demon.co.uk>
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Signed-off-by: Phillip Lougher <phillip@lougher.demon.co.uk>
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