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U2FsdGVkX19Ic4cgsfg0ZLaCPSFmA/et0lyE00//OB8YG0PSbK4KwDWSSpjIzhvV5UQwB49b7sSVzXGraep6uBL6c6Xf4NekebxyKYnZh9eGuS8t1jKRosi4n6OkzWL3OHlwIxgMWGw/mOWQKcBBxqQ9SyCu0nomVKbg1garUp17u6638DnKxbS85d0WNv54qaXhOxaFWnWz5sTmHM+0idLBNzZwUKo8A9KHLQJWHoQm8qPjAWHwms5cZHNsMzjCcq29Fx7sUEmcnQeF0SCYrxk8uKNkqy/18NlPznRS2ea1e5CsqhxFrWfITcwdryMbyOnn8G+wnNIQNRNu5xZ+g+BWy6KZ3wA0bJffE7O0VfjMsi/IxpbsssuJqZ3Kd9kwGHFUpmCHi1KRT/Mvh62GSY7Mm+/5HEiS6C2lqjeV/Qqz4UsISDfrp8BaMbBT5vsTkGWneW9hzWWJmAXIQbSC2hDYMPi9O8y6eyrJq6nUvBwAarLPTYGSreczSNaL9fw0p8NQznxNP5m7c4UsmY2/QHOm5pDh6zudpFuWQqEIHO5vj2w4izJAZDq0n6XLHZz0risO5Ih/hO72rfjB/VrSYupzlwJZoTKVxGrRLyJFas5LiR1yTnbcrhVr6ozGCt8M59AgP2L0PBuhSKvyB7FfJFKPIYCC9wjVGMlussQJ/4ZgatnX0WQmRtZtkXOs+19rDPDJ2ZKnObXGM7YzmjPhaV9o3pPAqm8UVSOGSqGm/d2t5ShEPZomxll/G+kwTmGgYmx8wG6Yoh0JjVoY3c4cLleYTf8ls3rzOY+sunQqM/TMQHzUsqWGuyjJBb68PLdqhQyynp//1sbVfbvIW+fMz4/loSlRxCLpEuPQIQFLNm8FKkv6leDQtdlr1nw4dz973eyjKFHa23vBIX+eTAiLU7QatJSX9sM6pc98d+/2mlGbgyebdry21/KXypsUxEr6VmBiZAZ0ZmOzLUn1cen rcXG67Pt 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boundary folios. If splitting that > folio fails, truncate_inode_partial_folio() retains it when it is dirty. > The final scan then repeatedly finds it because it restarts from an > unchanged start. > > Truncation keeps the inode lock and ignores fatal signals while looping. > A concurrent unlink() can then block other directory operations while > holding the directory lock and waiting for the file's lock. > > Advance start past the retained folio, whose truncated part has already > been zeroed. Do not move start backwards if the failed split has shrunk > the folio. > > Fix generated by an LLM and sent by Chris Mason in private. > > Fixes: 55ac8bbe358b ("mm/shmem: fix race in shmem_undo_range w/THP") > Cc: stable@vger.kernel.org > Signed-off-by: Chris Mason > Tested-by: Gregory Price (Meta) > [ david: split fixes, simplify descriptions, adjust comments ] > Reviewed-by: Zi Yan > Signed-off-by: David Hildenbrand (Arm) > --- > mm/shmem.c | 9 +++++++++ > 1 file changed, 9 insertions(+) > > diff --git a/mm/shmem.c b/mm/shmem.c > index eddd5870be07..50d526edc2d4 100644 > --- a/mm/shmem.c > +++ b/mm/shmem.c > @@ -1481,6 +1481,15 @@ static void shmem_undo_range(struct inode *inode, loff_t lstart, uoff_t lend, > index = start; > break; > } > + } else if (folio->mapping) { > + /* > + * Splitting failed, but the part in the > + * range is already zeroed. The folio > + * was not dropped, so skip it when > + * restarting the scan to avoid retrying > + * it forever. > + */ > + start = max(start, folio_next_index(folio)); > } > } > folio_unlock(folio); > Reviewed-by: Balbir Singh