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Gavin Shan b9792abb76 drivers/base/memory: Avoid overhead from for_each_present_section_nr() for_each_present_section_nr() was introduced to add_boot_memory_block() by commit `61659efdb3` ("drivers/base/memory: improve add_boot_memory_block()"). It causes unnecessary overhead when the present sections are really sparse. next_present_section_nr() called by the macro to find the next present section, which is far away from the spanning sections in the specified block. Too much time consumed by next_present_section_nr() in this case, which can lead to softlockup as observed by Aditya Gupta on IBM Power10 machine. watchdog: BUG: soft lockup - CPU#248 stuck for 22s! [swapper/248:1] Modules linked in: CPU: 248 UID: 0 PID: 1 Comm: swapper/248 Not tainted 6.15.0-rc1-next-20250408 #1 VOLUNTARY Hardware name: 9105-22A POWER10 (raw) 0x800200 opal:v7.1-107-gfda75d121942 PowerNV NIP: c00000000209218c LR: c000000002092204 CTR: 0000000000000000 REGS: c00040000418fa30 TRAP: 0900 Not tainted (6.15.0-rc1-next-20250408) MSR: 9000000002009033 <SF,HV,VEC,EE,ME,IR,DR,RI,LE> CR: 28000428 XER: 00000000 CFAR: 0000000000000000 IRQMASK: 0 GPR00: c000000002092204 c00040000418fcd0 c000000001b08100 0000000000000040 GPR04: 0000000000013e00 c000c03ffebabb00 0000000000c03fff c000400fff587f80 GPR08: 0000000000000000 00000000001196f7 0000000000000000 0000000028000428 GPR12: 0000000000000000 c000000002e80000 c00000000001007c 0000000000000000 GPR16: 0000000000000000 0000000000000000 0000000000000000 0000000000000000 GPR20: 0000000000000000 0000000000000000 0000000000000000 0000000000000000 GPR24: 0000000000000000 0000000000000000 0000000000000000 0000000000000000 GPR28: c000000002df7f70 0000000000013dc0 c0000000011dd898 0000000008000000 NIP [c00000000209218c] memory_dev_init+0x114/0x1e0 LR [c000000002092204] memory_dev_init+0x18c/0x1e0 Call Trace: [c00040000418fcd0] [c000000002092204] memory_dev_init+0x18c/0x1e0 (unreliable) [c00040000418fd50] [c000000002091348] driver_init+0x78/0xa4 [c00040000418fd70] [c0000000020063ac] kernel_init_freeable+0x22c/0x370 [c00040000418fde0] [c0000000000100a8] kernel_init+0x34/0x25c [c00040000418fe50] [c00000000000cd94] ret_from_kernel_user_thread+0x14/0x1c Avoid the overhead by folding for_each_present_section_nr() to the outer loop. add_boot_memory_block() is dropped after that. Fixes: `61659efdb3` ("drivers/base/memory: improve add_boot_memory_block()") Closes: https://lore.kernel.org/linux-mm/20250409180344.477916-1-adityag@linux.ibm.com Reported-by: Aditya Gupta <adityag@linux.ibm.com> Signed-off-by: Gavin Shan <gshan@redhat.com> Acked-by: Oscar Salvador <osalvador@suse.de> Tested-by: Aditya Gupta <adityag@linux.ibm.com> Acked-by: David Hildenbrand <david@redhat.com> Link: https://lore.kernel.org/r/20250410125110.1232329-1-gshan@redhat.com Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>		History 2025-04-15 18:19:49 +02:00
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README

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.