diff options
| -rw-r--r-- | fs/file.c | 30 |
1 files changed, 30 insertions, 0 deletions
diff --git a/fs/file.c b/fs/file.c index 97d212a9b814..c01c29417ae6 100644 --- a/fs/file.c +++ b/fs/file.c @@ -87,6 +87,21 @@ static void copy_fdtable(struct fdtable *nfdt, struct fdtable *ofdt) copy_fd_bitmaps(nfdt, ofdt, ofdt->max_fds); } +/* + * Note how the fdtable bitmap allocations very much have to be a multiple of + * BITS_PER_LONG. This is not only because we walk those things in chunks of + * '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) { struct fdtable *fdt; @@ -102,6 +117,7 @@ static struct fdtable * alloc_fdtable(unsigned int nr) nr /= (1024 / sizeof(struct file *)); nr = roundup_pow_of_two(nr + 1); nr *= (1024 / sizeof(struct file *)); + nr = ALIGN(nr, BITS_PER_LONG); /* * 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 @@ -269,11 +285,25 @@ static unsigned int count_open_files(struct fdtable *fdt) return i; } +/* + * Note that a sane fdtable size always has to be a multiple of + * BITS_PER_LONG, since we have bitmaps that are sized by this. + * + * 'max_fds' will normally already be properly aligned, but it + * turns out that in the close_range() -> __close_range() -> + * unshare_fd() -> dup_fd() -> sane_fdtable_size() we can end + * up having a 'max_fds' value that isn't already aligned. + * + * Rather than make close_range() have to worry about this, + * just make that BITS_PER_LONG alignment be part of a sane + * fdtable size. Becuase that's really what it is. + */ static unsigned int sane_fdtable_size(struct fdtable *fdt, unsigned int max_fds) { unsigned int count; count = count_open_files(fdt); + max_fds = ALIGN(max_fds, BITS_PER_LONG); if (max_fds < NR_OPEN_DEFAULT) max_fds = NR_OPEN_DEFAULT; return min(count, max_fds); |