linux-kernel - [PATCH 08/22] pidfs: expose coredump signal

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Message-Id: <20251028-work-coredump-signal-v1-8-ca449b7b7aa0@kernel.org>
Date: Tue, 28 Oct 2025 09:45:53 +0100
From: Christian Brauner <brauner@...nel.org>
To: linux-fsdevel@...r.kernel.org
Cc: 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>, 
 Alexander Mikhalitsyn <alexander@...alicyn.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>, 
 Christian Brauner <brauner@...nel.org>
Subject: [PATCH 08/22] pidfs: expose coredump signal

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>
---
 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