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/dump_stack.c | 131 +++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 131 insertions(+) create mode 100644 lib/dump_stack.c (limited to 'lib/dump_stack.c') diff --git a/lib/dump_stack.c b/lib/dump_stack.c new file mode 100644 index 000000000..f0c78b5b5 --- /dev/null +++ b/lib/dump_stack.c @@ -0,0 +1,131 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * Provide a default dump_stack() function for architectures + * which don't implement their own. + */ + +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include + +static char dump_stack_arch_desc_str[128]; + +/** + * dump_stack_set_arch_desc - set arch-specific str to show with task dumps + * @fmt: printf-style format string + * @...: arguments for the format string + * + * The configured string will be printed right after utsname during task + * dumps. Usually used to add arch-specific system identifiers. If an + * arch wants to make use of such an ID string, it should initialize this + * as soon as possible during boot. + */ +void __init dump_stack_set_arch_desc(const char *fmt, ...) +{ + va_list args; + + va_start(args, fmt); + vsnprintf(dump_stack_arch_desc_str, sizeof(dump_stack_arch_desc_str), + fmt, args); + va_end(args); +} + +#if IS_ENABLED(CONFIG_STACKTRACE_BUILD_ID) +#define BUILD_ID_FMT " %20phN" +#define BUILD_ID_VAL vmlinux_build_id +#else +#define BUILD_ID_FMT "%s" +#define BUILD_ID_VAL "" +#endif + +/** + * dump_stack_print_info - print generic debug info for dump_stack() + * @log_lvl: log level + * + * Arch-specific dump_stack() implementations can use this function to + * print out the same debug information as the generic dump_stack(). + */ +void dump_stack_print_info(const char *log_lvl) +{ + printk("%sCPU: %d UID: %u PID: %d Comm: %.20s %s%s %s %.*s %s " BUILD_ID_FMT "\n", + log_lvl, raw_smp_processor_id(), + __kuid_val(current_real_cred()->euid), + current->pid, current->comm, + kexec_crash_loaded() ? "Kdump: loaded " : "", + print_tainted(), + init_utsname()->release, + (int)strcspn(init_utsname()->version, " "), + init_utsname()->version, preempt_model_str(), BUILD_ID_VAL); + + if (get_taint()) + printk("%s%s\n", log_lvl, print_tainted_verbose()); + + if (dump_stack_arch_desc_str[0] != '\0') + printk("%sHardware name: %s\n", + log_lvl, dump_stack_arch_desc_str); + + print_worker_info(log_lvl, current); + print_stop_info(log_lvl, current); + print_scx_info(log_lvl, current); +} + +/** + * show_regs_print_info - print generic debug info for show_regs() + * @log_lvl: log level + * + * show_regs() implementations can use this function to print out generic + * debug information. + */ +void show_regs_print_info(const char *log_lvl) +{ + dump_stack_print_info(log_lvl); +} + +static void __dump_stack(const char *log_lvl) +{ + dump_stack_print_info(log_lvl); + show_stack(NULL, NULL, log_lvl); +} + +/** + * dump_stack_lvl - dump the current task information and its stack trace + * @log_lvl: log level + * + * Architectures can override this implementation by implementing its own. + */ +asmlinkage __visible void dump_stack_lvl(const char *log_lvl) +{ + bool in_panic = panic_on_this_cpu(); + unsigned long flags; + + /* + * Permit this cpu to perform nested stack dumps while serialising + * against other CPUs, unless this CPU is in panic. + * + * When in panic, non-panic CPUs are not permitted to store new + * printk messages so there is no need to synchronize the output. + * This avoids potential deadlock in panic() if another CPU is + * holding and unable to release the printk_cpu_sync. + */ + if (!in_panic) + printk_cpu_sync_get_irqsave(flags); + + __dump_stack(log_lvl); + + if (!in_panic) + printk_cpu_sync_put_irqrestore(flags); +} +EXPORT_SYMBOL(dump_stack_lvl); + +asmlinkage __visible void dump_stack(void) +{ + dump_stack_lvl(KERN_DEFAULT); +} +EXPORT_SYMBOL(dump_stack); -- cgit v1.3.1