From dd05add7b2b6004c5fa3a1f276f56d8668f86b65 Mon Sep 17 00:00:00 2001 From: Paulo Alcantara Date: Sat, 26 Sep 2026 19:20:30 -0300 Subject: netfs: zero the tail of a short DIO/unbuffered read The buffered read collector zero-fills the tail of a short read that stops below the inode's i_size (netfs_clear_unread()), so a read that races an extending write still returns the expected number of bytes. The non-buffered collector path does no such thing: it just records how much was transferred. Add the same zero-fill for the non-buffered case, gated on NETFS_SREQ_CLEAR_TAIL: a subreq's source sets that flag when a short result from it is known to be safe to treat as a hole, as opposed to NETFS_SREQ_HIT_EOF, which means the read genuinely ran off the end of the file and should be reported short as-is. Only CLEAR_TAIL should zero-fill here; a real EOF must stay a real short read. No source currently sets CLEAR_TAIL on an unbuffered/DIO subrequest, so this is inert on its own -- a following change teaches cifs to set it in the one case that needs it. Fixes: e2d46f2ec332 ("netfs: Change the read result collector to only use one work item") Reviewed-by: David Howells Reviewed-by: Namjae Jeon Signed-off-by: Paulo Alcantara Cc: Christian Brauner Cc: Matthew Wilcox Cc: Ronnie Sahlberg Cc: Shyam Prasad N Cc: Tom Talpey Cc: Bharath SM Cc: stable@vger.kernel.org --- lib/extable.c | 118 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 118 insertions(+) create mode 100644 lib/extable.c (limited to 'lib/extable.c') diff --git a/lib/extable.c b/lib/extable.c new file mode 100644 index 000000000..9c9f40bd2 --- /dev/null +++ b/lib/extable.c @@ -0,0 +1,118 @@ +// SPDX-License-Identifier: GPL-2.0-or-later +/* + * Derived from arch/ppc/mm/extable.c and arch/i386/mm/extable.c. + * + * Copyright (C) 2004 Paul Mackerras, IBM Corp. + */ + +#include +#include +#include +#include +#include +#include + +#ifndef ARCH_HAS_RELATIVE_EXTABLE +#define ex_to_insn(x) ((x)->insn) +#else +static inline unsigned long ex_to_insn(const struct exception_table_entry *x) +{ + return (unsigned long)&x->insn + x->insn; +} +#endif + +#ifndef ARCH_HAS_RELATIVE_EXTABLE +#define swap_ex NULL +#else +static void swap_ex(void *a, void *b, int size) +{ + struct exception_table_entry *x = a, *y = b, tmp; + int delta = b - a; + + tmp = *x; + x->insn = y->insn + delta; + y->insn = tmp.insn - delta; + +#ifdef swap_ex_entry_fixup + swap_ex_entry_fixup(x, y, tmp, delta); +#else + x->fixup = y->fixup + delta; + y->fixup = tmp.fixup - delta; +#endif +} +#endif /* ARCH_HAS_RELATIVE_EXTABLE */ + +/* + * The exception table needs to be sorted so that the binary + * search that we use to find entries in it works properly. + * This is used both for the kernel exception table and for + * the exception tables of modules that get loaded. + */ +static int cmp_ex_sort(const void *a, const void *b) +{ + const struct exception_table_entry *x = a, *y = b; + + /* avoid overflow */ + if (ex_to_insn(x) > ex_to_insn(y)) + return 1; + if (ex_to_insn(x) < ex_to_insn(y)) + return -1; + return 0; +} + +void sort_extable(struct exception_table_entry *start, + struct exception_table_entry *finish) +{ + sort(start, finish - start, sizeof(struct exception_table_entry), + cmp_ex_sort, swap_ex); +} + +#ifdef CONFIG_MODULES +/* + * If the exception table is sorted, any referring to the module init + * will be at the beginning or the end. + */ +void trim_init_extable(struct module *m) +{ + /*trim the beginning*/ + while (m->num_exentries && + within_module_init(ex_to_insn(&m->extable[0]), m)) { + m->extable++; + m->num_exentries--; + } + /*trim the end*/ + while (m->num_exentries && + within_module_init(ex_to_insn(&m->extable[m->num_exentries - 1]), + m)) + m->num_exentries--; +} +#endif /* CONFIG_MODULES */ + +static int cmp_ex_search(const void *key, const void *elt) +{ + const struct exception_table_entry *_elt = elt; + unsigned long _key = *(unsigned long *)key; + + /* avoid overflow */ + if (_key > ex_to_insn(_elt)) + return 1; + if (_key < ex_to_insn(_elt)) + return -1; + return 0; +} + +/* + * Search one exception table for an entry corresponding to the + * given instruction address, and return the address of the entry, + * or NULL if none is found. + * We use a binary search, and thus we assume that the table is + * already sorted. + */ +const struct exception_table_entry * +search_extable(const struct exception_table_entry *base, + const size_t num, + unsigned long value) +{ + return bsearch(&value, base, num, + sizeof(struct exception_table_entry), cmp_ex_search); +} -- cgit v1.3.1