5.10-stable patches

added patches:
	file-reinstate-f_pos-locking-optimization-for-regular-files.patch

diff --git a/queue-5.10/file-reinstate-f_pos-locking-optimization-for-regular-files.patch b/queue-5.10/file-reinstate-f_pos-locking-optimization-for-regular-files.patch
new file mode 100644 (file)
index 0000000..c12c8fb
--- /dev/null
+++ b/queue-5.10/file-reinstate-f_pos-locking-optimization-for-regular-files.patch
@@ -0,0 +1,64 @@
+From 797964253d358cf8d705614dda394dbe30120223 Mon Sep 17 00:00:00 2001
+From: Linus Torvalds <torvalds@linux-foundation.org>
+Date: Thu, 3 Aug 2023 11:35:53 -0700
+Subject: file: reinstate f_pos locking optimization for regular files
+
+From: Linus Torvalds <torvalds@linux-foundation.org>
+
+commit 797964253d358cf8d705614dda394dbe30120223 upstream.
+
+In commit 20ea1e7d13c1 ("file: always lock position for
+FMODE_ATOMIC_POS") we ended up always taking the file pos lock, because
+pidfd_getfd() could get a reference to the file even when it didn't have
+an elevated file count due to threading of other sharing cases.
+
+But Mateusz Guzik reports that the extra locking is actually measurable,
+so let's re-introduce the optimization, and only force the locking for
+directory traversal.
+
+Directories need the lock for correctness reasons, while regular files
+only need it for "POSIX semantics".  Since pidfd_getfd() is about
+debuggers etc special things that are _way_ outside of POSIX, we can
+relax the rules for that case.
+
+Reported-by: Mateusz Guzik <mjguzik@gmail.com>
+Cc: Christian Brauner <brauner@kernel.org>
+Link: https://lore.kernel.org/linux-fsdevel/20230803095311.ijpvhx3fyrbkasul@f/
+Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
+Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
+---
+ fs/file.c |   18 +++++++++++++++++-
+ 1 file changed, 17 insertions(+), 1 deletion(-)
+
+--- a/fs/file.c
++++ b/fs/file.c
+@@ -1007,12 +1007,28 @@ unsigned long __fdget_raw(unsigned int f
+       return __fget_light(fd, 0);
+ }
+ 
++/*
++ * Try to avoid f_pos locking. We only need it if the
++ * file is marked for FMODE_ATOMIC_POS, and it can be
++ * accessed multiple ways.
++ *
++ * Always do it for directories, because pidfd_getfd()
++ * can make a file accessible even if it otherwise would
++ * not be, and for directories this is a correctness
++ * issue, not a "POSIX requirement".
++ */
++static inline bool file_needs_f_pos_lock(struct file *file)
++{
++      return (file->f_mode & FMODE_ATOMIC_POS) &&
++              (file_count(file) > 1 || S_ISDIR(file_inode(file)->i_mode));
++}
++
+ unsigned long __fdget_pos(unsigned int fd)
+ {
+       unsigned long v = __fdget(fd);
+       struct file *file = (struct file *)(v & ~3);
+ 
+-      if (file && (file->f_mode & FMODE_ATOMIC_POS)) {
++      if (file && file_needs_f_pos_lock(file)) {
+               v |= FDPUT_POS_UNLOCK;
+               mutex_lock(&file->f_pos_lock);
+       }

diff --git a/queue-5.10/series b/queue-5.10/series
index 37d3b13e5c04dc205fce0eab5122b1fa7c5bdfa6..aaa344e5c41a6902f4f16d37106c811b693df8f9 100644 (file)
--- a/queue-5.10/series
+++ b/queue-5.10/series
@@ -173,3 +173,4 @@ net-tap_open-set-sk_uid-from-current_fsuid.patch
 bpf-disable-preemption-in-bpf_event_output.patch
 open-make-resolve_cached-correctly-test-for-o_tmpfile.patch
 drm-ttm-check-null-pointer-before-accessing-when-swapping.patch
+file-reinstate-f_pos-locking-optimization-for-regular-files.patch