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182db972c9
original report: https://lore.kernel.org/all/CAKhLTr1UL3ePTpYjXOx2AJfNk8Ku2EdcEfu+CH1sf3Asr=B-Dw@mail.gmail.com/T/ When doing buffered writes with FGP_NOWAIT, under memory pressure, the system returned ENOMEM despite there being plenty of available memory, to be reclaimed from page cache. The user space used io_uring interface, which in turn submits I/O with FGP_NOWAIT (the fast path). retsnoop pointed to iomap_get_folio: 00:34:16.180612 -> 00:34:16.180651 TID/PID 253786/253721 (reactor-1/combined_tests): entry_SYSCALL_64_after_hwframe+0x76 do_syscall_64+0x82 __do_sys_io_uring_enter+0x265 io_submit_sqes+0x209 io_issue_sqe+0x5b io_write+0xdd xfs_file_buffered_write+0x84 iomap_file_buffered_write+0x1a6 32us [-ENOMEM] iomap_write_begin+0x408 iter=&{.inode=0xffff8c67aa031138,.len=4096,.flags=33,.iomap={.addr=0xffffffffffffffff,.length=4096,.type=1,.flags=3,.bdev=0x… pos=0 len=4096 foliop=0xffffb32c296b7b80 ! 4us [-ENOMEM] iomap_get_folio iter=&{.inode=0xffff8c67aa031138,.len=4096,.flags=33,.iomap={.addr=0xffffffffffffffff,.length=4096,.type=1,.flags=3,.bdev=0x… pos=0 len=4096 This is likely a regression caused by66dabbb65d("mm: return an ERR_PTR from __filemap_get_folio"), which moved error handling from io_map_get_folio() to __filemap_get_folio(), but broke FGP_NOWAIT handling, so ENOMEM is being escaped to user space. Had it correctly returned -EAGAIN with NOWAIT, either io_uring or user space itself would be able to retry the request. It's not enough to patch io_uring since the iomap interface is the one responsible for it, and pwritev2(RWF_NOWAIT) and AIO interfaces must return the proper error too. The patch was tested with scylladb test suite (its original reproducer), and the tests all pass now when memory is pressured. Link: https://lkml.kernel.org/r/20250224143700.23035-1-raphaelsc@scylladb.com Fixes:66dabbb65d("mm: return an ERR_PTR from __filemap_get_folio") Signed-off-by: Raphael S. Carvalho <raphaelsc@scylladb.com> Reviewed-by: Christoph Hellwig <hch@lst.de> Reviewed-by: Dave Chinner <dchinner@redhat.com> Cc: "Darrick J. Wong" <djwong@kernel.org> Cc: Matthew Wilcow (Oracle) <willy@infradead.org> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
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.