--- /dev/null
+From 192e8b8d7e2f4ce941a89c1b5a5f3334fe8387d9 Mon Sep 17 00:00:00 2001
+From: Sasha Levin <sashal@kernel.org>
+Date: Tue, 6 Aug 2024 22:14:07 -0400
+Subject: alloc_fdtable(): change calling conventions.
+
+From: Al Viro <viro@zeniv.linux.org.uk>
+
+[ Upstream commit 1d3b4bec3ce55e0c46cdce7d0402dbd6b4af3a3d ]
+
+First of all, tell it how many slots do we want, not which slot
+is wanted. It makes one caller (dup_fd()) more straightforward
+and doesn't harm another (expand_fdtable()).
+
+Furthermore, make it return ERR_PTR() on failure rather than
+returning NULL. Simplifies the callers.
+
+Simplify the size calculation, while we are at it - note that we
+always have slots_wanted greater than BITS_PER_LONG. What the
+rules boil down to is
+ * use the smallest power of two large enough to give us
+that many slots
+ * on 32bit skip 64 and 128 - the minimal capacity we want
+there is 256 slots (i.e. 1Kb fd array).
+ * on 64bit don't skip anything, the minimal capacity is
+128 - and we'll never be asked for 64 or less. 128 slots means
+1Kb fd array, again.
+ * on 128bit, if that ever happens, don't skip anything -
+we'll never be asked for 128 or less, so the fd array allocation
+will be at least 2Kb.
+
+Reviewed-by: Christian Brauner <brauner@kernel.org>
+Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
+Signed-off-by: Sasha Levin <sashal@kernel.org>
+---
+ fs/file.c | 75 +++++++++++++++++++++----------------------------------
+ 1 file changed, 29 insertions(+), 46 deletions(-)
+
+diff --git a/fs/file.c b/fs/file.c
+index 4579c3296498..bfc9eb9e7229 100644
+--- a/fs/file.c
++++ b/fs/file.c
+@@ -90,18 +90,11 @@ static void copy_fdtable(struct fdtable *nfdt, struct fdtable *ofdt)
+ * 'unsigned long' in some places, but simply because that is how the Linux
+ * kernel bitmaps are defined to work: they are not "bits in an array of bytes",
+ * they are very much "bits in an array of unsigned long".
+- *
+- * The ALIGN(nr, BITS_PER_LONG) here is for clarity: since we just multiplied
+- * by that "1024/sizeof(ptr)" before, we already know there are sufficient
+- * clear low bits. Clang seems to realize that, gcc ends up being confused.
+- *
+- * On a 128-bit machine, the ALIGN() would actually matter. In the meantime,
+- * let's consider it documentation (and maybe a test-case for gcc to improve
+- * its code generation ;)
+ */
+-static struct fdtable * alloc_fdtable(unsigned int nr)
++static struct fdtable *alloc_fdtable(unsigned int slots_wanted)
+ {
+ struct fdtable *fdt;
++ unsigned int nr;
+ void *data;
+
+ /*
+@@ -109,22 +102,32 @@ static struct fdtable * alloc_fdtable(unsigned int nr)
+ * Allocation steps are keyed to the size of the fdarray, since it
+ * grows far faster than any of the other dynamic data. We try to fit
+ * the fdarray into comfortable page-tuned chunks: starting at 1024B
+- * and growing in powers of two from there on.
++ * and growing in powers of two from there on. Since we called only
++ * with slots_wanted > BITS_PER_LONG (embedded instance in files->fdtab
++ * already gives BITS_PER_LONG slots), the above boils down to
++ * 1. use the smallest power of two large enough to give us that many
++ * slots.
++ * 2. on 32bit skip 64 and 128 - the minimal capacity we want there is
++ * 256 slots (i.e. 1Kb fd array).
++ * 3. on 64bit don't skip anything, 1Kb fd array means 128 slots there
++ * and we are never going to be asked for 64 or less.
+ */
+- nr /= (1024 / sizeof(struct file *));
+- nr = roundup_pow_of_two(nr + 1);
+- nr *= (1024 / sizeof(struct file *));
+- nr = ALIGN(nr, BITS_PER_LONG);
++ if (IS_ENABLED(CONFIG_32BIT) && slots_wanted < 256)
++ nr = 256;
++ else
++ nr = roundup_pow_of_two(slots_wanted);
+ /*
+ * Note that this can drive nr *below* what we had passed if sysctl_nr_open
+- * had been set lower between the check in expand_files() and here. Deal
+- * with that in caller, it's cheaper that way.
++ * had been set lower between the check in expand_files() and here.
+ *
+ * We make sure that nr remains a multiple of BITS_PER_LONG - otherwise
+ * bitmaps handling below becomes unpleasant, to put it mildly...
+ */
+- if (unlikely(nr > sysctl_nr_open))
+- nr = ((sysctl_nr_open - 1) | (BITS_PER_LONG - 1)) + 1;
++ if (unlikely(nr > sysctl_nr_open)) {
++ nr = round_down(sysctl_nr_open, BITS_PER_LONG);
++ if (nr < slots_wanted)
++ return ERR_PTR(-EMFILE);
++ }
+
+ /*
+ * Check if the allocation size would exceed INT_MAX. kvmalloc_array()
+@@ -168,7 +171,7 @@ static struct fdtable * alloc_fdtable(unsigned int nr)
+ out_fdt:
+ kfree(fdt);
+ out:
+- return NULL;
++ return ERR_PTR(-ENOMEM);
+ }
+
+ /*
+@@ -185,7 +188,7 @@ static int expand_fdtable(struct files_struct *files, unsigned int nr)
+ struct fdtable *new_fdt, *cur_fdt;
+
+ spin_unlock(&files->file_lock);
+- new_fdt = alloc_fdtable(nr);
++ new_fdt = alloc_fdtable(nr + 1);
+
+ /* make sure all fd_install() have seen resize_in_progress
+ * or have finished their rcu_read_lock_sched() section.
+@@ -194,16 +197,8 @@ static int expand_fdtable(struct files_struct *files, unsigned int nr)
+ synchronize_rcu();
+
+ spin_lock(&files->file_lock);
+- if (!new_fdt)
+- return -ENOMEM;
+- /*
+- * extremely unlikely race - sysctl_nr_open decreased between the check in
+- * caller and alloc_fdtable(). Cheaper to catch it here...
+- */
+- if (unlikely(new_fdt->max_fds <= nr)) {
+- __free_fdtable(new_fdt);
+- return -EMFILE;
+- }
++ if (IS_ERR(new_fdt))
++ return PTR_ERR(new_fdt);
+ cur_fdt = files_fdtable(files);
+ BUG_ON(nr < cur_fdt->max_fds);
+ copy_fdtable(new_fdt, cur_fdt);
+@@ -322,7 +317,6 @@ struct files_struct *dup_fd(struct files_struct *oldf, struct fd_range *punch_ho
+ struct file **old_fds, **new_fds;
+ unsigned int open_files, i;
+ struct fdtable *old_fdt, *new_fdt;
+- int error;
+
+ newf = kmem_cache_alloc(files_cachep, GFP_KERNEL);
+ if (!newf)
+@@ -354,17 +348,10 @@ struct files_struct *dup_fd(struct files_struct *oldf, struct fd_range *punch_ho
+ if (new_fdt != &newf->fdtab)
+ __free_fdtable(new_fdt);
+
+- new_fdt = alloc_fdtable(open_files - 1);
+- if (!new_fdt) {
+- error = -ENOMEM;
+- goto out_release;
+- }
+-
+- /* beyond sysctl_nr_open; nothing to do */
+- if (unlikely(new_fdt->max_fds < open_files)) {
+- __free_fdtable(new_fdt);
+- error = -EMFILE;
+- goto out_release;
++ new_fdt = alloc_fdtable(open_files);
++ if (IS_ERR(new_fdt)) {
++ kmem_cache_free(files_cachep, newf);
++ return ERR_CAST(new_fdt);
+ }
+
+ /*
+@@ -413,10 +400,6 @@ struct files_struct *dup_fd(struct files_struct *oldf, struct fd_range *punch_ho
+ rcu_assign_pointer(newf->fdt, new_fdt);
+
+ return newf;
+-
+-out_release:
+- kmem_cache_free(files_cachep, newf);
+- return ERR_PTR(error);
+ }
+
+ static struct fdtable *close_files(struct files_struct * files)
+--
+2.50.1
+
projects / thirdparty / kernel / stable-queue.git / commitdiff
