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Message-ID: <CAJqdLro54iDWbR1P3hw_2AVLFPq4kSLcc85J_5u+OAifghUjyA@mail.gmail.com>
Date: Tue, 4 Nov 2025 09:45:57 +0100
From: Alexander Mikhalitsyn <alexander@...alicyn.com>
To: Christian Brauner <brauner@...nel.org>
Cc: linux-fsdevel@...r.kernel.org, Oleg Nesterov <oleg@...hat.com>,
Amir Goldstein <amir73il@...il.com>, Aleksa Sarai <cyphar@...har.com>,
Yu Watanabe <watanabe.yu+github@...il.com>, Josef Bacik <josef@...icpanda.com>,
Jeff Layton <jlayton@...nel.org>, Jann Horn <jannh@...gle.com>,
Luca Boccassi <luca.boccassi@...il.com>, linux-kernel@...r.kernel.org,
Alexander Viro <viro@...iv.linux.org.uk>, Jan Kara <jack@...e.cz>,
Lennart Poettering <lennart@...ttering.net>, Mike Yuan <me@...dnzj.com>,
Zbigniew Jędrzejewski-Szmek <zbyszek@...waw.pl>
Subject: Re: [PATCH 08/22] pidfs: expose coredump signal
Am Di., 28. Okt. 2025 um 09:46 Uhr schrieb Christian Brauner
<brauner@...nel.org>:
>
> Userspace needs access to the signal that caused the coredump before the
> coredumping process has been reaped. Expose it as part of the coredump
> information in struct pidfd_info. After the process has been reaped that
> info is also available as part of PIDFD_INFO_EXIT's exit_code field.
>
> Signed-off-by: Christian Brauner <brauner@...nel.org>
Reviewed-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@...onical.com>
> ---
> fs/pidfs.c | 30 +++++++++++++++++++-----------
> include/uapi/linux/pidfd.h | 7 +++++--
> 2 files changed, 24 insertions(+), 13 deletions(-)
>
> diff --git a/fs/pidfs.c b/fs/pidfs.c
> index a3b80be3b98b..354ceb2126e7 100644
> --- a/fs/pidfs.c
> +++ b/fs/pidfs.c
> @@ -41,6 +41,7 @@ void pidfs_get_root(struct path *path)
>
> enum pidfs_attr_mask_bits {
> PIDFS_ATTR_BIT_EXIT = 0,
> + PIDFS_ATTR_BIT_COREDUMP = 1,
> };
>
> struct pidfs_attr {
> @@ -51,6 +52,7 @@ struct pidfs_attr {
> __s32 exit_code;
> };
> __u32 coredump_mask;
> + __u32 coredump_signal;
> };
>
> static struct rb_root pidfs_ino_tree = RB_ROOT;
> @@ -297,7 +299,8 @@ static __u32 pidfs_coredump_mask(unsigned long mm_flags)
> PIDFD_INFO_CGROUPID | \
> PIDFD_INFO_EXIT | \
> PIDFD_INFO_COREDUMP | \
> - PIDFD_INFO_SUPPORTED_MASK)
> + PIDFD_INFO_SUPPORTED_MASK | \
> + PIDFD_INFO_COREDUMP_SIGNAL)
>
> static long pidfd_info(struct file *file, unsigned int cmd, unsigned long arg)
> {
> @@ -342,9 +345,12 @@ static long pidfd_info(struct file *file, unsigned int cmd, unsigned long arg)
> }
>
> if (mask & PIDFD_INFO_COREDUMP) {
> - kinfo.coredump_mask = READ_ONCE(attr->coredump_mask);
> - if (kinfo.coredump_mask)
> - kinfo.mask |= PIDFD_INFO_COREDUMP;
> + if (test_bit(PIDFS_ATTR_BIT_COREDUMP, &attr->attr_mask)) {
> + smp_rmb();
> + kinfo.mask |= PIDFD_INFO_COREDUMP | PIDFD_INFO_COREDUMP_SIGNAL;
> + kinfo.coredump_mask = attr->coredump_mask;
> + kinfo.coredump_signal = attr->coredump_signal;
> + }
> }
>
> task = get_pid_task(pid, PIDTYPE_PID);
> @@ -370,6 +376,7 @@ static long pidfd_info(struct file *file, unsigned int cmd, unsigned long arg)
>
> kinfo.coredump_mask = pidfs_coredump_mask(flags);
> kinfo.mask |= PIDFD_INFO_COREDUMP;
> + /* No coredump actually took place, so no coredump signal. */
> }
> }
>
> @@ -666,20 +673,21 @@ void pidfs_coredump(const struct coredump_params *cprm)
> {
> struct pid *pid = cprm->pid;
> struct pidfs_attr *attr;
> - __u32 coredump_mask = 0;
>
> attr = READ_ONCE(pid->attr);
>
> VFS_WARN_ON_ONCE(!attr);
> VFS_WARN_ON_ONCE(attr == PIDFS_PID_DEAD);
>
> - /* Note how we were coredumped. */
> - coredump_mask = pidfs_coredump_mask(cprm->mm_flags);
> - /* Note that we actually did coredump. */
> - coredump_mask |= PIDFD_COREDUMPED;
> + /* Note how we were coredumped and that we coredumped. */
> + attr->coredump_mask = pidfs_coredump_mask(cprm->mm_flags) |
> + PIDFD_COREDUMPED;
> /* If coredumping is set to skip we should never end up here. */
> - VFS_WARN_ON_ONCE(coredump_mask & PIDFD_COREDUMP_SKIP);
> - smp_store_release(&attr->coredump_mask, coredump_mask);
> + VFS_WARN_ON_ONCE(attr->coredump_mask & PIDFD_COREDUMP_SKIP);
> + /* Expose the signal number that caused the coredump. */
> + attr->coredump_signal = cprm->siginfo->si_signo;
> + smp_wmb();
> + set_bit(PIDFS_ATTR_BIT_COREDUMP, &attr->attr_mask);
> }
> #endif
>
> diff --git a/include/uapi/linux/pidfd.h b/include/uapi/linux/pidfd.h
> index e05caa0e00fe..ea9a6811fc76 100644
> --- a/include/uapi/linux/pidfd.h
> +++ b/include/uapi/linux/pidfd.h
> @@ -27,6 +27,7 @@
> #define PIDFD_INFO_EXIT (1UL << 3) /* Only returned if requested. */
> #define PIDFD_INFO_COREDUMP (1UL << 4) /* Only returned if requested. */
> #define PIDFD_INFO_SUPPORTED_MASK (1UL << 5) /* Want/got supported mask flags */
> +#define PIDFD_INFO_COREDUMP_SIGNAL (1UL << 6) /* Always returned if PIDFD_INFO_COREDUMP is requested. */
>
> #define PIDFD_INFO_SIZE_VER0 64 /* sizeof first published struct */
> #define PIDFD_INFO_SIZE_VER1 72 /* sizeof second published struct */
> @@ -94,8 +95,10 @@ struct pidfd_info {
> __u32 fsuid;
> __u32 fsgid;
> __s32 exit_code;
> - __u32 coredump_mask;
> - __u32 __spare1;
> + struct /* coredump info */ {
> + __u32 coredump_mask;
> + __u32 coredump_signal;
> + };
> __u64 supported_mask; /* Mask flags that this kernel supports */
> };
>
>
> --
> 2.47.3
>
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