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 --- Documentation/admin-guide/init.rst | 48 ++++++++++++++++++++++++++++++++++++++ 1 file changed, 48 insertions(+) create mode 100644 Documentation/admin-guide/init.rst (limited to 'Documentation/admin-guide/init.rst') diff --git a/Documentation/admin-guide/init.rst b/Documentation/admin-guide/init.rst new file mode 100644 index 000000000..41f06a091 --- /dev/null +++ b/Documentation/admin-guide/init.rst @@ -0,0 +1,48 @@ +Explaining the "No working init found." boot hang message +========================================================= +:Authors: Andreas Mohr + Cristian Souza + +This document provides some high-level reasons for failure +(listed roughly in order of execution) to load the init binary. + +1) **Unable to mount root FS**: Set "debug" kernel parameter (in bootloader + config file or CONFIG_CMDLINE) to get more detailed kernel messages. + +2) **init binary doesn't exist on rootfs**: Make sure you have the correct + root FS type (and ``root=`` kernel parameter points to the correct + partition), required drivers such as storage hardware (such as SCSI or + USB!) and filesystem (ext3, jffs2, etc.) are builtin (alternatively as + modules, to be pre-loaded by an initrd). + +3) **Broken console device**: Possibly a conflict in ``console= setup`` + --> initial console unavailable. E.g. some serial consoles are unreliable + due to serial IRQ issues (e.g. missing interrupt-based configuration). + Try using a different ``console= device`` or e.g. ``netconsole=``. + +4) **Binary exists but dependencies not available**: E.g. required library + dependencies of the init binary such as ``/lib/ld-linux.so.2`` missing or + broken. Use ``readelf -d |grep NEEDED`` to find out which libraries + are required. + +5) **Binary cannot be loaded**: Make sure the binary's architecture matches + your hardware. E.g. i386 vs. x86_64 mismatch, or trying to load x86 on ARM + hardware. In case you tried loading a non-binary file here (shell script?), + you should make sure that the script specifies an interpreter in its + shebang header line (``#!/...``) that is fully working (including its + library dependencies). And before tackling scripts, better first test a + simple non-script binary such as ``/bin/sh`` and confirm its successful + execution. To find out more, add code ``to init/main.c`` to display + kernel_execve()s return values. + +Please extend this explanation whenever you find new failure causes +(after all loading the init binary is a CRITICAL and hard transition step +which needs to be made as painless as possible), then submit a patch to LKML. +Further TODOs: + +- Implement the various ``run_init_process()`` invocations via a struct array + which can then store the ``kernel_execve()`` result value and on failure + log it all by iterating over **all** results (very important usability fix). +- Try to make the implementation itself more helpful in general, e.g. by + providing additional error messages at affected places. + -- cgit v1.3.1